Metric System FAQ

Markus Kuhn

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May 1, 2004, 10:17:04 AM5/1/04

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Metric System FAQ
-----------------

This regular posting to the USENET group misc.metric-system provides a
brief introduction, collects useful references, and answers some
frequently asked questions.

A note on the character set: This file was written and distributed in
the Unicode UTF-8 encoding. If "©" does not show up as a copyright
sign, chances are that the encoding has been corrupted on the way to
you or that your news reader lacks support for the MIME or UTF-8
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Suggestions for improvement are welcome! ☺

Markus Kuhn
http://www.cl.cam.ac.uk/~mgk25/

Contents
--------

1 Basics

1.1 What is the International System of Units (SI)?
1.2 What is the history of the metric system?
1.3 Which countries have yet to fully adopt the metric system?
1.4 What are the advantages of the metric system?
1.5 How can I make myself more familiar with the metric system?
1.6 Where are good web sites related to the metric system?
1.7 Are there any good books or newsletters on the metric system?
1.8 What are the SI base units and how are they currently defined?
1.9 What are the SI derived units with a special name?
1.10 Who were the SI units named after?
1.11 What are the SI prefixes?
1.12 What is the correct way of writing metric units?

2 Metric product specifications

2.1 What are preferred numbers or Renard numbers?
2.2 How do metric paper sizes work?
2.3 How do metric threads work?
2.4 How do metric clothes sizes work?
2.5 What inch-based standards are widely used in metric countries?
2.5.1 Metric water-pipe thread designations
2.5.2 Metric bicycle tire and rim designations
2.5.3 Shotgun gauge sizes
2.6 What metric standards are commonly known under an inch name?

3 Misc

3.1 Why is there a newsgroup on the metric system?
3.2 Where can I look up unit conversion factors?
3.3 What is the exact international definition of some non-SI units?
3.4 What are calories?
3.5 What are FFUs and WOMBAT units?
3.6 Does kilo mean 1024 in computing?
3.7 What are the official short symbols for bit and byte?
3.8 What does the "e" symbol found on many packaged goods mean?

1 Basics
=========

1.1 What is the International System of Units (SI)?
---------------------------------------------------

The "International System of Units" is the modern definition of what
is colloquially known in the English-speaking world as the "metric
system". Its name is commonly abbreviated as "SI", short for the
French "Le Système International d'Unites".

The SI is built on the seven base units metre, kilogram, second,
ampere, kelvin, mole, and candela for measuring length, mass, time,
electric current, thermodynamic temperature, amount of substance and
luminosity.

Units for measuring all other quantities are derived in the SI by
multiplying and dividing these base units. This leads to a "coherent"
system of units that almost eliminates the need for unit conversion
factors in calculations. A list of 22 derived SI units have names of
their own, for example newton, pascal, joule, volt, ohm, and watt.

In order to provide conveniently sized units for all applications, the
SI defines a set of prefixes -- such as milli, micro, nano, kilo,
mega, and giga -- that can be used to derive decimal multiples or
submultiples of units. The use of SI prefixes introduces conversion
factors in calculations, but these are all powers of ten, which are
trivial to apply in mental arithmetic by shifting the decimal point.

1.2 What is the history of the metric system?
----------------------------------------------

A very brief scientific history of the metric system:

The origin of the SI dates back to the early 1790s, when a coherent
system of weights and measures with decimal multiples and fractions
was proposed in France. On 22 June 1799, two platinum standards
representing the metre and the kilogram were deposited in Paris. In
1832, the German astronomer Gauss made a strong case for the use of
the metric system in the physical sciences and proposed extensions for
measuring magnetic fields. The British physicists Maxwell and Thomson
led in 1874 the extension of Gauss' proposal to the CGS. This system
of units for electromagnetic theory was derived from the base units
centimetre, gram and second and found some use in experimental
physics. However, the sizes of some of the CGS units turned out to be
inconvenient. This lead in the 1880s in British and international
scientific organizations to the development of a variant system with
the base units metre, kilogram and second, known as MKS. This system
introduced the modern electricity units volt, ampere, and ohm. In
1901, the Italian physicist Giorgi proposed a minor modification of
the MKS system, turning the ampere into a fourth base unit, leading to
the MKSA system of units that became internationally accepted after
long discussions in 1946. In 1954 two more base units for temperature
(kelvin) and luminosity (candela) were added to the MKSA system, which
was renamed in 1960 into the International System of Units (SI).
Finally, in 1971, the SI as it is used today was completed by adding
the mole as the base unit for amount of substance.

A very brief legal history of the metric system:

Metric units became the only legally accepted weights and measures in
Belgium, the Netherlands, and Luxembourg in 1820, followed by France
in 1837. They were rapidly adopted between 1850 and 1900 across Europe
(except for the United Kingdom) and Latin America. The metric system
became the subject of an international treaty, the Metre Convention of
1875, which created the International Bureau of Weights and Measures
(Bureau International des Poids et Mesures, BIPM) in Paris that became
in charge of its maintenance. Its exact definition has since then been
periodically reviewed and revised by the International Conference of
Weights and Measures (Conférence Générale des Poids et Mesures,
CGPM). It continued to spread around the world during the first half
of the 20th century. Among the last developed countries to convert
were South Africa, Australia, New Zealand and Canada in the early
1970s.

1.3 Which countries have yet to fully adopt the metric system?
---------------------------------------------------------------

British industry converted successfully to the metric system in the
1960s. But with continued legal validity of inch-pound units, takeup
of the metric system by the British public remained a slow process for
three decades, which is still in progress. The pound finally lost its
status as a legal weight in the United Kingdom on 1 January 2000. The
legal use of non-metric units is now limited to a few special fields:

- mile, yard, foot or inch for road traffic signs, distance
and speed measurement

- pint for dispensing draught beer and cider

- pint for milk in returnable containers

- acre for land registration

- troy ounce for transactions in precious metals

- units used in international conventions for air and sea transport

[http://www.legislation.hmso.gov.uk/si/si1995/Uksi_19951804_en_1.htm]

British media coverage continues to use non-metric units frequently
alongside metric units, in particular feet and inches for the size of
humans and stones for their weight. Weather reports add the occasional
Fahrenheit temperature as a courtesy to the older generation, but air
temperature is predominantly reported in degrees Celsius today.

Progress in the Republic of Ireland is somewhat faster than in
Britain. In particular, road signs use at present a mixture of
imperial and metric units and are scheduled to be fully metric by the
end of 2004.

The United States is today the last country in which the use of
inch-pound units is required by law in many areas. Most other
countries do not even legally recognize inch-pound units. US media
coverage still uses almost exclusively inch-pound-fahrenheit units. A
dual labeling requirement for retail products was introduced in
1992. A lobbying campaign "Coalition for Permissible Metric-Only
Labeling" supported by several large US manufacturers is now underway
to make the use of inch-pound units in consumer products optional in
federal law. The proposed change would allow manufacturers to simplify
US labels such as "24 fl. oz. (1 Pint 8 fl. oz.) 710 mL" to something
as neat and globally acceptable as "710 mL". US manufacturers suffer
at the moment the problem that the US customary units for volume,
which are mandatory in the US, differ from the Imperial units of the
same name and are therefore illegal for use in the United
Kingdom. This leads to separate labels and causes additional costs for
US manufacturers who want to export to the UK.

Canada has switched to the metric system in the late 1970s, but
inch-pound units remain some part of daily life in Canada due to its
close economic ties with the US. For example, Canada is the only other
country in the world that uses the US "Letter" paper size instead of
the international standard A4 format.

If your teacher has asked you to find out which three countries have
not yet introduced the metric system, chances are that the expected
answer is "United States, Liberia and Burma" (the last of these is
called Myanmar today). This answer is almost certainly out of
date. The widely-quoted statement that these are the last three
countries not to have introduced the metric system may have originated
in some 1970s US government report and appears to have been mentioned
for a while in the CIA World Factbook. Although the introduction of
the metric system is clearly slowest in the US compared to any other
developed country, it is widely used today in the US in selected
areas. Little authoritative information can be found on what the legal
or customary units are in Liberia and Burma today. Anecdotal evidence
from visitors and trading partners suggests that both are essentially
metric. The misc.metric-system readers are still eagerly awaiting
knowledgeable first-hand reports from people living in these
countries.

1.4 What are the advantages of the metric system?
-------------------------------------------------

This question comes up in misc.metric-system usually in discussions
with Americans who see no compelling reason for why the United States
should make a serious effort to abandon their customary inch-pound
units and move on to the metric system.

The most frequently given answers include:

- Because practically everyone uses it

Americans who have never left their country may not realize that
their customary system of inch-pound units is today practically
unknown in most countries. For more than 95% of the world
population, the metric system is the customary system of units,
and for more than half of the industrialized world, it has been
for at least a century. Products designed in non-metric units or
using non-metric standards can cause serious maintenance and
compatibility problems for customers in major world markets and do
place a manufacturer at a disadvantage.

- Because using two incompatible systems causes unnecessary friction

The United States lacks a coherent system of units. Economic
realities, international standards, and the short-comings of the
inch-pound system (e.g., lack of electrical and chemical units,
lack of small subunits) force it already to use the metric system
alongside its customary inch-pound units. American students waste
at least half a year of math education with developing
unit-conversion skills (both within the inch-pound system and
between inch-pound and metric) that are utterly irrelevant in the
metric-only rest of the world. [The study "Education System
Benefits of U.S. Metric Conversion", by Richard P. Phelps,
published in Evaluation Review, February 1996, estimated that
teaching solely metric measurements could save 82 days of maths
instruction-time annually, worth over 17 billion dollars.]

- Because it dramatically reduces conversion factors in calculations

In spite of a significant amount of secondary school time being
wasted in the United States in science and math education with
training the use of conversion factors between the bewildering set
of units in use there, only few educated Americans know by heart
how to convert between gallons and cubic feet or inches and miles.
The inch-pound system suffers from a bewildering, random and
completely unsystematic set of conversion factors between units
for the same quantity, for instance 1 mile = 1760 yards and 1 US
gallon = 231 cubic inches. It also suffers from the use of too
many different units for the same quantity. Energy alone, for
example, is measured in the US in calories, british thermal units,
ergs, feet pound-force, quads, terms, tons of TNT, kilowatt-hours,
electron volts, and joules, and power is measured in ergs per
second, foot pound-force per second, several types of horsepowers,
and watts.

Users of the metric system, on the other hand, have to use
conversion factors only where there are significant physical
reasons for using alternative units to express some situation. An
example is the choice between molar concentration (a count of
molecules better describes a chemical reaction balance) and a mass
concentration (which describes better how a pharmacist prepares
medication) in medicine. The main other reason for using
conversion factors in the metric world is the continued use of
non-decimal multiples of the second (hour, day, year).

- Because metric dimensions are easier to divide by three

A commonly brought up but misleading claim is that the inch-pound
system supports division by three. While it is true that the
factor three appears in the inch-foot and foot-yard conversion
factors, this argument fails for the rest of the system. In
practice, people find that metric dimensions are far easier to
subdivide by various factors, as it is easier to move to smaller
subunits and as it is more common in the metric world to use
standardized preferred number sequences. For example, in the
British building industry, it is normal to chose major design
dimensions (e.g., grid lines on a building plan) as multiples of
60 or 600 mm. As a result, common building dimensions can be
divided by 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 25, 30, 40, 50,
60, 75, 100, 120, 150, 200, and 300 without having to resort to
millimetre fractions. Even without such precautions, it is
instantly obvious that one kilometre divided three is 333 1/3
metres and 1/3 L = 333 1/3 mL, whereas even inch-pound enthusiasts
are a bit pressed when asked what 1/3 mile is in yards (answer:
586 2/3) or what 1/3 lb is in ounces (5 1/3). Furthermore, while
the use of decimal fractions is preferred in the metric system,
because this simplifies the mental conversion between different
units prefixes, there is no reason why vulgar fractions cannot be
used where it seems appropriate.

- Because it is the only properly maintained system

The inch-pound system as used in the United States has essentially
stopped evolving more than 200 years ago when the metric system
emerged. Although it would in principle have been possible to
extend the inch-pound system into a coherent and even decimal
system of units, this never happened. The US customary system of
units uses the inch and pound only for mechanical quantities. It
had to copy, for example, all its electrical units (volt, ampere,
watt, ohm) from the metric system. The length of the inch still
differed noticeably between several English-speaking countries as
late as World War II, which interfered with the exchange of
precision equipment. It had to be redefined in 1959, when 1 inch
finally became 25.4 mm, at which point industries in all
English-speaking countries -- apart from the United States --
decided to abandon the inch entirely for precision work and later
also for general use.

1.5 How can I make myself more familiar with the metric system?
----------------------------------------------------------------

The metric system is today universally used in Britain, and even the
United States, in science, medicine, and in many industries
(electronics, automobile, etc.). But as long as inch-pound units
appear in the media and in consumer communication (advertisement,
product labels), many people will end up feeling more familiar with
them, in particular the generation that went through secondary
education before the 1970s.

Good knowledge of a few important reference values make units easy to
visualize, even where they are not yet encountered in daily life. This
list is a suggestion of approximate metric values that every educated
adult may want to be familiar with. Also useful for trivial-pursuit
type games.

A) Humans

Typical height of an adult: 1.60-1.90 m
Typical weight of an adult: 50-90 kg

[The "body mass index (BMI)" is the weight in kilograms divided by
the height in metres squared. BMI values of 18-25 kg/m² are
considered normal, values outside this range mean an increased
disease risk.]

Keeping in mind that the size of most adults varies by about 20%,
the following are easy to remember estimates for typical values:

Width of an adult hand or foot: 10 cm

Width of the nail of the small finger: 1 cm

Maximum distance between elbows: 1 m

Height of the hip above ground: 1 m

Length of a moderately large step: 1 m

Foot length: 25 cm

Daily energy needed: 10 MJ (men)
8 MJ (women)

Energy of a healthy meal: 2 MJ

Daily water needed: 2 L

Blood volume: 5 L

Lung capacity: 5 L

B) General Physics

Speed of sound: 340 m/s

Speed of light: 300 000 km/s

Acceleration of free fall (Earth): 10 m/s²

Atmospheric pressure (Earth): 100 kPa

Density of water: 1000 kg/m³ = 1 kg/L

C) Geology and Astronomy

Distance pole to equator (Earth): 10 000 km = 10 Mm

Length of the Earth equator: 40 000 km = 40 Mm

Altitude of geostationary Earth orbit: 36 000 km = 36 Mm

Distance Earth-Sun: 150 Gm

Diameter of solar system: 12 Tm

Diameter of our galaxy: 1 Zm

Distance to most distant visible objects: 100 Ym

D) Traffic

Walking speed 5 km/h

Cycling speed 20 km/h

Speed limit in traffic-calmed areas: 30 km/h

Speed limits on urban roads: 50-60 km/h

Speed limits on rural roads: 60-80 km/h

Speed limits on highways: 90-130 km/h

Long-distance average car speed: 100 km/h

Cruise altitude of passenger planes: 10 000 m = 10 km

Cruise speed of passenger planes: 600-800 km/h

E) Temperatures

Lowest possible temperature: -273.15 °C = 0 K

Typical freezer temperature: -18 °C

Freezing water/melting ice: 0 °C

Preferred soft drink temperature (US): 0 °C

Temperature of highest density of water: 4 °C

Typical fridge temperature: 4-8 °C

Comfortable office room temperature: 20-25 °C
(same for swimming-pool water)

Hot day: 25-35 °C
(same for baby bath water)

Body temperature: 37 °C

Fever temperatures: 38-40 °C

Deadly fever: 41-42 °C

Proteins denaturate starting from: 45-50 °C
(in cooking: egg becomes solid)

Food poisoning bacteria might grow: 5-55 °C

Food poisoning bacteria die: 60 °C

Flour absorbs most water starting at: 70 °C
(minimum temperature dough/batter needs
to reach in any kind of baking)

Alcohol boils: 78 °C

Best temperature for green tea (Japan): 80 °C

Water boils: 100 °C

Typical baking-oven air temperature: 150-220 °C

Washing machine settings: 30, 40, 50, 60, 95 °C

F) Angles

While degrees remain popular and useful for large angles (30°, 45°,
60°, 90°, etc.), the radian is extremely convenient and intuitive
for small angles, for example those covered by a pixel of a digital
camera.

1 mm seen from 1 m distance: 1 mrad
1 mm seen from 1 km distance: 1 µrad
1 m at the end of the universe: 0.01 yrad

The steradian is used mostly in the context of describing the
intensity of radiation.

1 mm² seen from 1 m distance: 1 µsr
1 mm² seen from 1 km distance: 1 psr

1.6 Where are good web sites related to the metric system?
-----------------------------------------------------------

The Bureau International des Poids et Mesures (BIPM) is the
international organization in charge of maintaining the International
System of Units:

http://www.bipm.org/

The BIPM's "SI Brochure" is the official 72-page in-depth description
of the International System of Units:

http://www.bipm.org/en/publications/brochure/

The Physics Laboratory of the US National Institute of Science and
Technology (NIST) maintains an excellent web site on SI units:

http://physics.nist.gov/cuu/Units/

In particular, NIST has published three highly recommendable guides to
the SI:

- The first focuses on the practical use of the SI in the United
States, and features a very comprehensive conversion table for all
units used in the United States, as well as detailed guidelines
for the correct spelling, abbreviation and typesetting of SI unit
names:

Guide for the Use of the International System of Units (SI)
NIST Special Publication 811, 1995 Edition, by Barry N. Taylor.
http://physics.nist.gov/Pubs/SP811/

- The second is simply the official United States version of the
English SI brochure, which provides more information on the
history of the SI:

The International System of Units (SI)
NIST Special Publication 330, 2001 Edition, Barry N. Taylor, Editor.
http://physics.nist.gov/Pubs/SP330/

- Finally, for those looking for the legal definition of the SI in
U.S. legislation, there is:

Interpretation of the International System of Units for
the United States, Federal Register notice of July 28, 1998,
63 FR 40334-40340
http://physics.nist.gov/Document/SIFedReg.pdf

The Laws & Metric Group of NIST's Weights and Measures Division also
maintains a comprehensive site on the metric system, with a particular
focus on its legal role and history in the United States:

http://www.nist.gov/metric

The UK's National Physics Laboratory (NPL) has some SI information:

http://www.npl.co.uk/reference/

The U.S. Metric Association (USMA) is a non-profit organization
founded in 1916 that advocates U.S. conversion to the International
System of Units:

http://lamar.colostate.edu/~hillger/

Its British counterpart, the UK metric association (UKMA), was founded
in 1999:

http://www.metric.org.uk/

Two excellent online dictionaries of units are:

http://www.unc.edu/~rowlett/units/
http://www.sizes.com/units/

Other interesting web sites related to the metric system:

http://www.metrication.com/
http://www.metre.info/

1.7 Are there any good books or newsletters on the metric system?
------------------------------------------------------------------

A fascinating book on the history of the metre and the considerations
that led to its creation is:

Ken Alder: The Measure of All Things. Free Press, October 2003,
ISBN 0743216768.

In June 1792, amidst the chaos of the French Revolution, two intrepid
astronomers set out in opposite directions on an extraordinary
journey. Starting in Paris, Jean-Baptiste-Joseph Delambre would make
his way north to Dunkirk, while Pierre-François-André Méchain voyaged
south to Barcelona. Their mission was to measure the world, and their
findings would help define the metre as one ten-millionth of the
distance between the pole and the equator -- a standard that would be
used "for all people, for all time."

A very useful reference not only on the correct use of SI units, but
on international standard conventions for mathematical and scientific
notation in general is:

ISO Standards Handbook: Quantities and units. 3rd ed., International
Organization for Standardization, Geneva, 1993, 345 p.,
ISBN 92-67-10185-4, 182.00 CHF
http://www.iso.org/iso/en/prods-services/otherpubs/links/quantities.html

This unfortunately rather expensive book contains the full text
of the following ISO standards:

ISO 31:1992 Quantities and units

Part 0: General principles
Part 1: Space and time
Part 2: Periodic and related phenomena
Part 3: Mechanics
Part 4: Heat
Part 5: Electricity and magnetism
Part 6: Light and related electromagnetic radiations
Part 7: Acoustics
Part 8: Physical chemistry and molecular physics
Part 9: Atomic and nuclear physics
Part 10: Nuclear reactions and ionizing radiations
Part 11: Mathematical signs and symbols for use in
the physical sciences and technology
Part 12: Characteristic numbers
Part 13: Solid state physics

ISO 1000:1992 SI units and recommendations for the use of their
multiples and of certain other units

ISO 31 standardizes a significant part of the mathematical notation
used in physical sciences and technology worldwide. Its various
parts contains a pretty comprehensive table of physical quantities
(e.g., speed, mass, frequency, resistance), and defines for each the
standard variable name (e.g., v, m, f, R) that is normally used in
textbooks, together with the appropriate SI unit and a brief
explanation of the meaning of the quantity. ISO 31-0 contains
detailed guidelines on how to use and write SI units in mathematical
formulas and ISO 31-11 defines all the commonly used mathematical
symbols and operators.

ISO 1000 is a brief summary of the SI (shorter than ISO 31-0), plus
an appendix that lists for some selected quantities and units the
more commonly used prefixes.

Especially authors and editors of scientific textbooks, teaching
material and reference works that use SI units should make sure that
they have easy access to a copy of ISO 31 or an equivalent national
standard (e.g., BS 5775 in Britain).

The unfortunately not less expensive German equivalent is:

DIN-Taschenbuch 22: Einheiten und Begriffe für physikalische
Größen. Deutsches Institut für Normung, 1999-03,
ISBN 3-410-14463-3, 98.90 EUR

A list of books on metrication is on:

http://www.metrication.com/products/books.htm

Members of the U.S. Metric Association receive six times a year the
"Metric Today" newsletter with detailed updates on the progress of
metrication in the US. Membership costs 30 USD anually (35 USD
abroad).

http://lamar.colostate.edu/~hillger/mtoday.htm
http://lamar.colostate.edu/~hillger/member.htm

A very comprehensive book on current and historic units from all over
the world is

François Cardarelli: Encyclopaedia of scientific units,
weights and measures: their SI equivalences and origins.
Springer, 2003, 872 pages, ISBN 1-85233-682-X.

1.8 What are the SI base units and how are they currently defined?
-------------------------------------------------------------------

length: metre (m)

The metre is the length of the path travelled by light in vacuum
during a time interval of 1/299 792 458 of a second.

[Originally, the metre was chosen to approximate the distance
between the north pole and the equator divided by ten million, such
that a unit that is roughly the size of a step can also help to
visualize large distances on the surface of the earth easily.]

mass: kilogram (kg)

The kilogram is the unit of mass; it is equal to the mass of the
international prototype of the kilogram.

[No independent lab experiment is known yet that provides a more
stable reference for mass than the regular comparison with a lump of
platinum-iridium alloy kept in a safe at the BIPM in Paris.]

[Originally, the kilogram was chosen to approximate the mass of one
litre (1/1000 m³) of water. This choice, combined with the second,
also led to very convenient numbers for the Earth's gravity (about
10 m/s²) and atmospheric pressure (about 100 kPa).]

time: second (s)

The second is the duration of 9 192 631 770 periods of the radiation
corresponding to the transition between the two hyperfine levels of
the ground state of the caesium 133 atom.

[In other words: if you want to know how long a second is, buy an
atomic clock that uses caesium, such as the classic Agilent/HP 5071A.]

[Originally, the SI second was chosen to approximate the length of
the astronomical second (1 day divided by 60 × 60 × 24) around 1820.]

electric current: ampere (A)

The ampere is that constant current which, if maintained in two
straight parallel conductors of infinite length, of negligible
circular cross-section, and placed 1 m apart in vacuum, would
produce between these conductors a force equal to 2 × 10^-7 newton
per metre of length.

[In other words, the ampere is defined by setting the magnetic
permeability of free space to 4π × 10^-7 H/m. This way,
electromagnetic equations concerning spheres contain 4π, those
concerning coils contain 2π and those dealing with straight wires
lack π entirely.]

thermodynamic temperature: kelvin (K)

The kelvin, unit of thermodynamic temperature, is the fraction
1/273.16 of the thermodynamic temperature of the triple point of
water.

[The celsius temperature scale divides the temperature interval of
liquid water into 100 steps. The kelvin has the same size as the
degree celsius, but its origin is moved to the lowest possible
temperature (0 K = -273.15 °C) to simplify gas calculations and
avoid negative numbers. The triple point of water at 0.01 °C is a
more well-defined reference temperature than its melting temperature
at some arbitrarily chosen pressure.]

amount of substance: mole (mol)

1. The mole is the amount of substance of a system which contains as
many elementary entities as there are atoms in 0.012 kilogram of
carbon 12.

2. When the mole is used, the elementary entities must be specified
and may be atoms, molecules, ions, electrons, other particles, or
specified groups of such particles.

[No technique is known yet to accurately count the number of
molecules in a macroscopic amount of matter, therefore the current
definition of the mole is no better than the definition of the
kilogram.]

luminous intensity: candela (cd)

The candela is the luminous intensity, in a given direction, of a
source that emits monochromatic radiation of frequency 540 × 10^12
hertz and that has a radiant intensity in that direction of 1/683
watt per steradian.

[This is a psychophysical unit for describing how bright an average
human eye perceives some electromagnetic radiation in the optical
frequency bands. As such, it differs very much from the purely
physical nature of the other units. The definition of the SI base
unit for luminous intensity provides merely a calibration value that
replaces an older one based on a reference candle. It has to be used
together with sensitivity models of an average human eye that have
been standardized by CIE. Many other physiological units are in use,
such as the "phon" for perceived loudness and the "bark" for
perceived audio frequency in acoustics, but none of these have made
it into the SI, possibly because it is much more difficult to reach
a consensus in audiology.]

1.9 What are the SI derived units with a special name?
-------------------------------------------------------

Derived quantity unit name symbol in terms of base or
other derived units

plane angle radian rad 1 rad = 1 m/m = 1
solid angle steradian sr 1 sr = 1 m²/m² = 1
frequency hertz Hz 1 Hz = 1 1/s
force newton N 1 N = 1 kg·m/s²
pressure, stress pascal Pa 1 Pa = 1 N/m²
energy, work, heat joule J 1 J = 1 N·m
power watt W 1 W = 1 J/s
electric charge coulomb C 1 C = 1 A·s
electric potential volt V 1 V = 1 W/A
capacitance farad F 1 F = 1 C/V
electric resistance ohm Ω 1 Ω = 1 V/A
electric conductance siemens S 1 S = 1 1/Ω
magnetic flux weber Wb 1 Wb = 1 V·s
magnetic fluc density tesla T 1 T = 1 Wb/m²
inductance henry H 1 H = 1 Wb/A
Celsius temperature deg. Celsius °C 1 °C = 1 K
luminous flux lumen lm 1 lm = 1 cd·sr
illuminance lux lx 1 lx = 1 lm/m²

Note: We have 0 °C = 273.15 K and temperature differences of 1 °C and
1 K are identical. Kelvin and degrees Celsius values can be converted
into each other by adding or subtracting the number 273.15. The origin
of the degrees Celsius scale is set 0.01 K below the triple-point
temperature of water (273.16 K) and approximates the freezing
temperature of water at standard pressure.

Three more SI derived units have been defined for use in radiology and
radioactive safety:

radioactivity becquerel Bq 1 Bq = 1 1/s
absorbed dose gray Gy 1 Gy = 1 J/kg
dose equivalent sievert Sv 1 Sv = 1 J/kg

Note: Different types of radiation (α, β, γ, X-rays, neutrons, etc.)
vary in the amount of damage they cause in biological tissue, even
when the same energy is absorbed. While the physical unit gray is used
to describe just the energy absorbed, the medical unit sievert is used
where the absorbed energy has been multiplied with a quality factor to
quantify the health risk better. This quality factor is 1 for X-rays,
γ-rays, electrons, and muons. It goes up to 20 for heavier
particles. [Details in ICRU Report 51 from http://www.icru.org/.]

Note: only those unit symbols start with an uppercase letter where the
name of the corresponding unit was derived from the name of a person.

The following eight units are not SI units, but are accepted to be
commonly used with or instead of SI units:

time minute min 1 min = 60 s
hour h 1 h = 60 min
day d 1 d = 24 h
plane angle degree ° 1° = (π/180) rad
minute ' 1' = (1/60)°
second " 1" = (1/60)'
volume litre l, L 1 l = 1 dm³
mass ton t 1 t = 1000 kg

Note: The litre would normally be abbreviated with a lowercase l, as
it is not named after a person. However, the US interpretation of the
SI prefers the capital letter L instead, to avoid confusion between l
and 1.

Note: The SI ton is also called "tonne" or "metric ton" in some
English-speaking countries where other tons are still in use, to avoid
confusion.

The following two units acceptable for use with or instead of SI
units have values that are obtained experimentally:

energy electron volt eV 1 eV = energy acquired by
an electron passing
through 1 V potential
difference
mass atomic unit u 1 u = 1/12 of the mass of
one carbon-12 atom

1.10 Who were the SI units named after?
----------------------------------------

André Marie Ampère France 1775-1836
Lord Kelvin (Sir William Thomson) Britain 1824-1907
Sir Isaac Newton Britain 1643-1727
Heinrich Hertz Germany 1857-1894
Blaise Pascal France 1623-1662
James Prescott Joule Britain 1818-1889
James Watt Britain 1736-1819
Charles Augustin de Coulomb France 1736-1806
Alessandro Volta Italy 1745-1827
Michael Faraday Britain 1791-1867
Georg Simon Ohm Germany 1787-1854
Werner von Siemens Germany 1816-1892
Wilhelm Eduard Weber Germany 1804-1891
Nikola Tesla USA 1856-1943
Joseph Henry USA 1797-1878
Anders Celsius Sweden 1701-1744
Antoine Henri Becquerel France 1852-1908
Louis Harold Gray Britain 1905-1965
Rolf Maximilian Sievert Sweden 1896-1966

1.11 What are the SI prefixes?
-------------------------------

Some rules about writing and using SI prefixes are worth remembering:

- The symbols for the prefix kilo and everything below start with a
lowercase letter, whereas mega and higher use an uppercase
letter.

[The reason why the boundary between lowercase and uppercase has
been moved between kilo and mega is the fact that that kilo also
appears in the unit kilogram, whose symbol must start with a
lowercase letter to follow the rule that only units named after
people are abbreviated with an uppercase symbol.]

- SI prefixes bind to a unit stronger than any mathematical
operator, that is 1 km² means a kilometre squared (as in 1 (km)²)
and not one kilosquaremeter (as in 1 k(m²)).

- SI prefixes are not allowed to be used on anything other than an
unprefixed unit, in other words there is no such thing as a
megakilometre or a kilosquaremetre.

1.12 What is the correct way of writing metric units?
------------------------------------------------------

Each unit and prefix in the International System of Units has an
official symbol (abbreviation) assigned to it. This symbol is
identical in all languages. When writing down numeric quantities,
especially in the more formal context of product descriptions,
documentation, signs, scientific publications, etc., it is important
to pay some attention to the accurate writing of the unit symbol.

Here are the most important rules for abbreviating SI units:

- Use exactly the standard symbols for prefixes and units listed
in the tables above. Do not invent your own abbreviations.

- Remember that there is a simple system for deciding which letters
are uppercase or lowercase:

- Symbols of units named after a person start uppercase.
(E.g., newton, volt, weber use N, V, Wb.)
- Other units start lowercase.
(E.g., metre, second, lux use m, s, lx.)
- Symbols of prefixes greater than 10³ (kilo) start uppercase.
- All other prefix symbols start with a lowercase letter.
- Further letters in a unit or prefix are always lowercase.

(Correct examples: kHz, MHz)

- Unit symbols are never used with a plural s.

- Units symbols are never used with a period to indicate
an abbreviation.

- Division can be indicated by either a stroke (slash) or by a
negative exponent, but never by a "p" for "per".

- Square and cube are indicated by exponents 2 and 3, respectively.

- The unit symbol is separated from the preceding number by a space
character (with the exception of degrees, minutes and seconds of
plane angle: 90° 13' 59").

- There is no space between a prefix and a unit.

- In mathematical and technical writing, SI unit symbols should be
typeset in an upright font, in order to distinguish them from
variables, which are usually set in an italic font.

Examples:

Good: 60 km/h, 3.2 kHz, 40 kg, 3.6 mm, 80 g/m²

Bad: 60 kph, 3.2 Khz, 40 kgs, 3.6mm, 80-grms./sq.mtr.

Whether a decimal comma (French, German, etc.) or decimal point
(English) is used depends on the language. Either is valid for use
with SI units. To avoid confusion, neither the comma nor the dot
should be used to group digits together. Better use a space character,
if necessary.

Good: 12 000 m
Bad: 12,000 m (might be read as 12 m in France and 12 km in the US)

Hints for word processing users:

- The degree sign (° as in °C and 360°, Unicode U+00B0) is in some
fonts easily confused with the Spanish masculine ordinal indicator
sign (º, a raised little letter "o", as in 1º for "premiero",
Unicode U+00BA). In other fonts, the Spanish raised o is clearly
distinguishable because it is underlined. It is therefore
important, especially where the author has no control over the
font used by the reader (email, web, etc.), to pick the correct
character.

Good: °C
Bad: ºC

- The micro sign (µ) is at Unicode position U+00B5 (decimal: 181)
and can be entered under Microsoft's Windows by pressing 0181 on
the numeric keypad while pressing the Alt key.

Other characters not found on every keyboard can be entered as
well by entering the decimal Unicode value preceded by zero on the
numeric keypad, while holding down the Alt key:

Character Unicode value Unicode value Character
name hexadecimal decimal

no-break space U+00A0 160
degree sign U+00B0 176 °
superscript 2 U+00B2 178 ²
superscript 3 U+00B3 179 ³
micro sign U+00B5 181 µ
ohm sign U+2126 8486 Ω

Some keyboards with AltGr key provide these characters also via
AltGr-d, AltGr-2, AltGr-3, AltGr-m, or similar combinations.

While the short symbols for SI units are internationally standardized,
at least for all languages that use the Latin alphabet, the spelling
of unit names varies between languages and even countries. In
English, unabbreviated unit names are not capitalized, even where they
are named after people, and both the French -re and the Germanic -er
ending of metre and litre are commonly used.

Examples:

French German English (GB) English (US)

litre Liter litre liter
metre Meter metre meter

This FAQ uses the British English spellings of metre and litre, as
they are used in ISO and BIPM documents.

Some countries that do not use the Latin alphabet have standardized
their own short symbols for SI units. The Russian standard GOST
8.417:1981, for example, specifies Cyrillic symbols м (m), кг (kg),
с (s), А (A), К (K), моль (mol), кд (cd), etc. (Full list on
<http://www.unics.uni-hannover.de/ntr/russisch/si-einheiten.html>.)

There used to exist an international standard ISO 2955:1983
("Presentation of SI and other units in systems with limited character
sets") that defined a list of unambiguous SI symbols for use with
computers that can only display ASCII, or even only uppercase
letters. This standard was withdrawn 2001. The ISO 8859-1 and ISO
10646 character sets are today widely enough available to make using
the original SI symbols on computers feasible.

There is no international standard for pronouncing the names of
units. In particular, in English both KILL-o-metr and ki-LO-metr are
commonly used. The former seems to be more common in Britain (short
stress on the first syllable) and may have the slight advantage of
being consistent with the English pronunciation of kilogram and
kilohertz. (It is also the pronunciation of kilometre in other
Germanic languages.)

In spoken language, various colloquial short forms have evolved for SI
units. For example, "kilo", "hecto" and "deca" are used in various
countries for 1 kg, 100 g and 10 g when buying groceries. In the US
military, a "klick" is 1 km or 1 km/h, depending on the context, and
in the semiconductor industry a "micron" is 1 µm. A "kay" can be heard
in some English-speaking countries referring to any of 1 km, 1 km/h, 1
kg, 1 kHz, 1 kB, 1 kbit/s, again depending on the context. A "pound"
refers to 500 g in many European countries, but it is less commonly
used today than a decade or two ago. But none of these colloquial
forms should be used in writing.

2 Metric product specifications
================================

2.1 What are preferred numbers or Renard numbers?
-------------------------------------------------

Product developers need to decide at some point, how large various
characteristic dimensions of their design will be exactly. Even after
taking into account all known restrictions and considerations, the
exact choice of lengths, diameters, volumes, etc. can often still be
picked quite randomly within some interval.

Wouldn't it be nice if there were some recipe or guideline for making
the choice of product dimensions less random? If there were one
generic standard for a small set of preferred numbers, it would be
more likely that a developer working in a different company made the
same choice. Products would more frequently become compatible by
chance. Say you design a gadget that will be fixed on a wall with two
screws. A small set of preferred distances between mounting screws
would make it less likely that new holes have to be drilled if your
customer replaces an older gadget of similar size, whose designer
hopefully chose the same distance.

The French army engineer Col. Charles Renard proposed in the 1870s
such a set of preferred numbers for use with the metric system, which
became in 1952 the international standard ISO 3. Renard's preferred
numbers divide the interval from 1 to 10 into 5, 10, 20, or 40
steps. The factor between two consecutive numbers in a Renard series
is constant (before rounding), namely the 5th, 10th, 20th or 40 root
of 10 (1.58, 1.26, 1.12, and 1.06, respectively), leading to a
geometric series. This way, the maximum relative error is minimized if
an arbitrary number is replaced by the nearest Renard number
multiplied by the appropriate power of 10.

The most basic R5 series consists of these five rounded numbers:

R5: 1.00 1.60 2.50 4.00 6.30

Example: If our design constraints tell us that the two screws in our
gadget can be spaced anywhere between 32 mm and 55 mm apart, we make
it 40 mm, because 4 is in the R5 series of preferred numbers.

Example: If you want to produce a set of nails with lengths between
roughly 15 and 300 mm, then the application of the ISO 3 R5 series
would lead to a product repertoire of 16 mm, 25 mm, 40 mm, 63 mm, 100
mm, 160 mm and 250 mm long nails.

If a finer resolution is needed, another five numbers are added and we
end up with the R10 series:

R10: 1.00 1.25 1.60 2.00 2.50 3.15 4.00 5.00 6.30 8.00

If you design several prototypes of a product that may later have to
be offered in several additional sizes, choosing characteristic
dimensions from the Renard numbers will make sure that your prototypes
will later fit nicely into an evenly spaced product repertoire.

Where higher resolution is needed, the R20 and R40 series can be
applied:

R20: 1.00 1.12 1.25 1.40 1.60 1.80 2.00 2.24 2.50 2.80
3.15 3.55 4.00 4.50 5.00 5.60 6.30 7.10 8.00 9.00

R40: 1.00 1.06 1.12 1.18 1.25 1.32 1.40 1.50 1.60 1.70
1.80 1.90 2.00 2.12 2.24 2.36 2.50 2.65 2.80 3.00
3.15 3.35 3.55 3.75 4.00 4.25 4.50 4.75 5.00 5.30
5.60 6.00 6.30 6.70 7.10 7.50 8.00 8.50 9.00 9.50

In some applications more rounded values are desirable, either
because the numbers from the normal series would imply an
unrealistically high accuracy, or because an integer value is needed
(e.g., the number of teeth in a gear). For these, the more rounded
versions of the Renard series have been defined:

R5': 1 1.5 2.5 4 6

R10': 1 1.25 1.6 2 2.5 3.2 4 5 6.3 8

R10": 1 1.2 1.5 2 2.5 3 4 5 6 8

R20': 1 1.1 1.25 1.4 1.6 1.8 2 2.2 2.5 2.8
3.2 3.6 4 4.5 5 5.6 6.3 7.1 8 9

R20": 1 1.1 1.2 1.4 1.6 1.8 2 2.2 2.5 2.8
3 3.5 4 4.5 5 5.5 6 7 8 9

R40': 1 1.05 1.1 1.2 1.25 1.3 1.4 1.5 1.6 1.7
1.8 1.9 2 2.1 2.2 2.4 2.5 2.6 2.8 3
3.2 3.4 3.6 3.8 4 4.2 4.5 4.8 5 5.3
5.6 6 6.3 6.7 7.1 7.5 8 8.5 9 9.5

Other more specialized preferred number schemes are in use in various
fields. For example:

- IEC 63 standardizes a preferred number series for resistors and
capacitors, a variant of the Renard series that subdivides the
interval from 1 to 10 into 6, 12, 24, etc. steps. These
subdivisions ensure that when some random value is replaced with
the nearest preferred number, the maximum error will be in the
order of 20%, 10%, 5%, etc.:

E6 (20%): 10 15 22 33 47 68

E12 (10%): 10 12 15 18 22 27 33 39 47 56 68 82

E24 ( 5%): 10 11 12 13 15 16 18 20 22 24 27 30
33 36 39 43 47 51 56 62 68 75 82 91

- Paper sizes commonly use factors of sqrt(2), sqrt(sqrt(2)), or
sqrt(sqrt(sqrt(2))) as factors between neighbor dimensions
(Lichtenberg series, see next section). The sqrt(2) factor also
appears between the standard metric pen thicknesses for technical
drawings (0.13, 0.18, 0.25, 0.35, 0.50, 0.70, 1.00, 1.40, and 2.00
mm). This way, the right pen size is available to continue a
drawing that has been magnified to a different metric paper size.

- In the British building industry, major grid lines on plans are
often spaced a multiple of 600 mm apart, a value with a
particularly high number of small factors.

- In computer engineering, the powers of two (1, 2, 4, 8, 16, ...)
multiplied by 1, 3 or 5 are frequently used as preferred numbers.
These correspond to binary numbers that consist mostly of trailing
zero bits, which are particularly easy to add and subtract in
hardware. [Software developers should keep in mind though that
using powers of 2 in software, especially with array sizes, may
also have disadvantages, such as reduced CPU cache efficiency.]

2.2 How do metric paper sizes work?
------------------------------------

The international standard paper formats defined in ISO 216 in the A,
B and C series are used today in all countries worldwide except for
the US and Canada.

The formats have been defined as follows:

- The width divided by the height of all ISO A, B, and C formats
is the square root of 2 (= 1.41421...)

- The A0 paper size has an area of one square metre.

- You get the next higher format number by cutting the paper in two
equal pieces (cutting parallel to the shorter side). The result will
again have a 1 : sqrt(2) format (that's the big advantage of this format).

- The size of a B-series paper is the geometric mean between the size of
the corresponding A-series paper and the next bigger A-series paper.
For example, the same magnification factor converts from A1 to B1
and from B1 to A0.

- The size of a C-series paper is the geometric mean between the size of
the A-series and B-series paper with the same number.

This means that the following formulas give the dimensions in metres:

Width Height
A-series 2 ^ (- 1/4 - n/2) 2 ^ (1/4 - n/2)
B-series 2 ^ ( - n/2) 2 ^ (1/2 - n/2)
C-series 2 ^ (- 1/8 - n/2) 2 ^ (3/8 - n/2)

Larger sizes have smaller numbers.

The official definitions of the ISO paper formats are obtained by
rounding down to the next lower integer millimetre after each
division:

4 A0 1682 × 2378
2 A0 1189 × 1682
A0 841 × 1189 B0 1000 × 1414 C0 917 × 1297
A1 594 × 841 B1 707 × 1000 C1 648 × 917
A2 420 × 594 B2 500 × 707 C2 458 × 648
A3 297 × 420 B3 353 × 500 C3 324 × 458
A4 210 × 297 B4 250 × 353 C4 229 × 324
A5 148 × 210 B5 176 × 250 C5 162 × 229
A6 105 × 148 B6 125 × 176 C6 114 × 162
A7 74 × 105 B7 88 × 125 C7 81 × 114
A8 52 × 74 B8 62 × 88 C8 57 × 81
A9 37 × 52 B9 44 × 62 C9 40 × 57
A10 26 × 37 B10 31 × 44 C10 28 × 40

The most popular sizes are perhaps:

A0 technical drawings
A4 letters, forms, faxes, magazines, documents
A5, B5 books
C4, C5, C6 envelopes
B4, A3 supported by many copy machines, newspapers

There are also strip formats possible for tickets, compliment cards,
etc.:

1/3 A4 99 × 210
2/3 A4 198 × 210
1/4 A4 74 × 210
1/8 A4 37 × 210
1/4 A3 105 × 297
1/3 A5 70 × 148
etc.

All these formats are end formats, i.e. these are the dimensions of
the paper delivered to the user/reader. Other standards define
slightly bigger paper sizes for applications where the paper will be
cut to the end format later (e.g. after binding).

The A4 format used in almost all countries is 6 mm narrower and 18 mm
taller than the US Letter format used exclusively in the US and
Canada. This difference causes an enormous amount of havoc every day
in document exchange with these countries. The introduction of A4
paper as the general office format in the United States would be a
very significant simplification and an enormous improvement. Only a
top-level US government decision is likely to make this happen.

For much more information, for example on how the Japanese JIS B sizes
differ from the ISO ones, see

http://www.cl.cam.ac.uk/~mgk25/iso-paper.html

2.3 How do metric threads work?
--------------------------------

The preferred ISO metric thread sizes for general purpose fasteners
(coarse thread) are

designation pitch tapping drill clearance holes
close medium free

M1.6 0.35 1.25 1.7 1.8 2.0
M2 0.4 1.6 2.2 2.4 2.6
M2.5 0.45 2.05 2.7 2.9 3.1
M3 0.5 2.5 3.2 3.4 3.6
M4 0.7 3.3 4.3 4.5 4.8
M5 0.8 4.2 5.3 5.5 5.8
M6 1.0 5.0 6.4 6.6 7.0
M8 1.25 6.8 8.4 9.0 10.0
M10 1.5 8.5 10.5 11.0 12.0
M12 1.75 10.2 13.0 14.0 15.0
M16 2.0 14.0 17.0 18.0 19.0
M20 2.5 17.5 21.0 22.0 24.0
M24 3.0 21.0 25.0 26.0 28.0
M30 3.5 26.5 31.0 33.0 35.0
M36 4.0 32.0 37.0 39.0 42.0
M42 4.5 37.5 43.0 45.0 48.0
M48 5.0 43.0 50.0 52.0 56.0

The number naming the thread is the major diameter of the screw thread
in millimetres. The thread angle is 60°. The pitch is the distance
that the screw will travel during one rotation in millimetres.

The preferred standard pitch defined for each M-series thread is
called the "coarse pitch". For special applications (e.g., thin wall
tubes), there are also "fine pitch" variants defined. In their
designation, the pitch is added after a cross (×), as in

M8×1, M10×1, M12×1.5, ...

[This section is work in progress ... contributions welcome.]

http://www.metrication.com/engineering/threads.htm
http://www.efunda.com/DesignStandards/screws/screwm_coarse.cfm

2.4 How do metric clothes sizes work?
--------------------------------------

Even in Europe, most clothes are currently still labelled using some
ad-hoc dress size number that has no obvious or even well-defined
relation with actual body dimensions. The European standards bodies
are currently trying to push forward a new system of metric cloth
sizes. Ad-hoc dress sizes vary significantly between countries, many
are inadequate because they are based on obsolete 1950s data, and some
manufacturers have started to inflate women's dress sizes to
compensate for the average weight gain of middle ages adults. As a
result, dress sizes have lost much of their usefulness, especially for
mail and online ordering.

The new system is defined in European Standard EN 13402. The core
ideas are:

Clothes are labelled based on body dimensions in centimetres of the
wearer. EN 13402-1 defines a standard list of body dimensions that can
be used in clothes labels, together with an anatomical explanation and
measurement guidelines:

head girth: maximum horizontal girth of the head measured
above the ears

neck girth: girth of the neck measured with the tape-measure
passed 2 cm below the Adam's apple and at the
level of the 7th cervical vertebra

chest girth: maximum horizontal girth measured during normal
breathing with the subject standing erect and
the tape-measure passed over the shoulder blades
(scapulae), under the armpits (axillae), and
across the chest

bust girth: maximum horizontal girth measured during normal
breathing with the subject standing erect and
the tape-measure passed horizontally, under the
armpits (axillae), and across the bust
prominence underbust girth: horizontal girth of
the body measured just below the breasts
[Preferably measured with moderate tension over
a brassiere that shall not deform the breast
in an unnatural way and shall not displace its
volume.]

underbust girth: horizontal girth of the body measured just below
the breasts

waist girth: girth of the natural waistline between the top
of the hip bones (iliac crests) and the lower
ribs, measured with the subject breathing
normally and standing erect with the abdomen
relaxed

hip girth: horizontal girth measured round the buttocks at
the level of maximum circumference

height: vertical distance between the crown of the head
and the soles of the feet, measured with the
subject standing erect without shoes and with
the feet together (for infants not yet able to
stand upright: length of the body measured in a
straight line from the crown of the head to the
soles of the feet)

inside leg length: distance between the crotch and the soles of the
feet, measured in a straight vertical line with
the subject erect, feet slightly apart, and the
weight of the body equally distributed on both
legs

arm length: distance, measured using the tape-measure, from
the armscye/shoulder line intersection
(acromion), over the elbow, to the far end of
the prominent wrist bone (ulna), with the
subject's right fist clenched and placed on the
hip, and with the arm bent at 90°

hand girth: maximum girth measured over the knuckles
(metacarpals) of the open right hand, fingers
together and thumb excluded

foot length: horizontal distance between perpendiculars in
contact with the end of the most prominent toe
and the most prominent part of the heel,
measured with the subject standing barefoot and
the weight of the body equally distributed on
both feet

body mass: measured with a suitable balance in kilograms

[The standard also clarifies that these dimensions are meant to be
measured preferably without or as few as possible clothes.]

EN 13402-1 also defines a standard pictogram that can be used on
language-neutral labels to indicate one or several of these body
dimensions. [See http://www.cl.cam.ac.uk/~mgk25/download/bodydim.pdf
for some software to draw such pictograms.]

EN 13402-2 defines for each type of garment a "primary dimension"
according to which it should be labelled (e.g. head girth for a
bicycle helmet or height for a pyjama). For some types of garnment,
where a single size is not adequate to select the right product, a
secondary dimension is added (e.g. inside leg length and waist girth
for trousers).

EN 13402-3 is under final review and is expected to complete the new
European metric clothes sizes system in 2004. It will define, for each
type of garnment, preferred numbers of primary and secondary body
dimensions, from which the manufacturer can then chose. Several large
anthropometric studies are currently being completed to find the best
set of dimension ranges and step sizes for this part of the standard.

Two related press releases by the British Standards Institute:

http://www.bsi-global.com/News/Releases/2002/March/n3f02c7044524a.xalter
http://www.bsi-global.com/News/Releases/2003/October/n3f9953e58c3df.xalter

Professional dress and personal protection equipment has for many
years been labelled with metric body dimensions, based on ISO
standards very similar to EN 13402-1. It can be hoped that the
completion of the remaining parts of EN 13402 will boost the use of
metric clothes sizes also on the high street.

[The British retailer Marks & Spencer has already a trial run of
metric clothes sizes going on.]

2.5 What inch-based standards are widely used in metric countries?
-------------------------------------------------------------------

2.5.1 Metric water-pipe thread designations:

The ISO 228 pipe threads used all over the world in domestic water and
heating systems are based on the British Standard pipe (BSP) threads.
They use a Whitworth (55°) thread with an integral number of threads
per inch (i.e., the thread pitch divides 25.4 mm evenly). The standard
specifies today the exact thread parameters in millimetres and the
threads and pipes are named after the nominal bore (inner) diameter of
the pipe, which defines its flow capacity. This nominal bore diameter
for each standard pipe thread can be given in either inches or
millimetres. The actual bore diameter is usually somewhere in between
the equivalent inch and millimetre names for each pipe and it is not
tightly linked to the corresponding thread dimensions. None of the
actual dimensions of these threads are exactly round inch or
millimetre values. The outer diameter of an 8 mm pipe will typically
be about 14 mm, for example. The following table lists the equivalent
inch and metric nominal bore diameters after which the ISO 228 pipe
threads are named:

Just to clarify: the thread on the end of an "8 mm pipe" (outer thread
diameter 13.157 mm) has nothing to do with the ISO metric thread of an
M8 bolt (outer thread diameter 8 mm).

2.5.2 Metric bicycle tire and rim designations:

Many of the bicycle tires and rims used all over the world are based
on older British inch-based standards. However, their dimensions are
defined and labelled today in millimetres according to the
international standard format defined in ISO 5775.

For example, a normal "wired edge" tire (for straight-side and
crotchet-type rims) with a "nominal section width" of 32 mm, a
"nominal rim diameter" of 597 mm, and a "recommended inflation
pressure" of 400 kPa is marked according to ISO 5775-1 as:

32-597 inflate to 400 kPa

The first number (nominal section width) is essentially the width of
the inflated tire (minus any tread) in millimetres. The inner width of
the rim on which the tire is mounted should be about 65% of the tire's
nominal section width for tires smaller than 30 mm and 55% for those
larger. The second number (nominal rim diameter) is essentially the
inner diameter of the tire in millimetres when it is mounted on the
rim. The corresponding circumference can be measured with a suitably
narrow tape inside the rim.

The minimum inflation pressure recommended for a "wired edge" tire is
300 kPa for narrow tires (25 mm section width or less), 200 kPa for
other sizes in normal highway service, and 150 kPa for off-the-road
service.

More information: http://www.cl.cam.ac.uk/~mgk25/iso-5775.html

2.5.3 Shotgun gauge sizes

Shotgun barrel diameters are in many countries still named using a
historic "gauge" scale. An n-gauge diameter means that n balls of
lead (density 11.352 g/cm³) with that diameter weigh one pound
(453.5924 g). Therefore an n-gauge shotgun has a barrel diameter

d = [6 × 453.59237 g / (11.352 g/cm³ × n × π)] ^ 1/3
= 42.416 mm / (n ^ 1/3)

2.6 What metric standards are commonly known under an inch name?
-----------------------------------------------------------------

- The so-called "3.5 inch floppy disk" (ISO 9529) is in fact a fully
metric design, originally developed by Sony in Japan. It was first
introduced on the market as the "90 mm floppy disk", and it is
exactly 90 mm wide, 94 mm long, and 3.3 mm thick. The disk inside
has a diameter of 85.8 mm. Not a single dimension of this disk
design is 3.5 in (88.9 mm).

[The older 5 1/4 and 8 inch floppies, on the other hand, are
inch-based designs by IBM.]

- The standard silicon wafers known in the US as 6, 8, or 12 inch
wafers are actually 150 mm, 200 mm and 300 mm in diameter (SEMI
M1-1103).

- People unfamiliar with the ISO 3 preferred number system sometimes
suspect wrongly that a -- to them -- unusual looking measured
millimetre dimension is actually an inch dimension, whereas the
designer chose in fact a metric length from a Renard series:

Renard dimension popular inch dimension

25 mm (R5) 1 inch = 25.4 mm
12 mm (R5) 1/2 inch = 12.7 mm
6.3 mm (R5) 1/4 inch = 6.35 mm
3.15 mm (R10) 1/8 inch = 3.175 mm

3 Misc
=======

3.1 Why is there a newsgroup on the metric system?
---------------------------------------------------

The USENET newsgroup was created in December 2003 after a ballot for
its creation had passed on 25 November 2003 with 211 yes votes against
25 no votes. The charter of this worldwide unmoderated electronic
discussion forum sums up its scope:

This newsgroup is for discussion about the International System of
Units (SI) or metric system, including its use in scientific,
technical, and consumer applications, its history and definition, and
its adoption in fields and regions where other units of measurement
are still prevalent (metrication). Included within its scope are
related global standards and conventions, for example metric product
specifications and consumer-product labelling practice.

The proposal to create the group noted:

Units of measurement and related standards affect many aspects of our
daily lives. The global standardization of a single consistent
International System of Units was a major breakthrough for human
civilization and significantly simplified communication, learning,
work and trade all over the planet.

The introduction of the metric system still faces delays in some
areas. Notable examples are consumer communication and traffic
regulations in the United States and United Kingdom, as well as parts
of the aeronautical and typographic industry. It is therefore no
surprise that discussions about the metric system flare up regularly
in many different newsgroups. In particular the slow progress with
metrication in the United States promises to fuel such debates for
many years to come.

A dedicated newsgroup will focus expertise and will provide a medium
for professionals and hobbyists to find advice and suggestions on
metric product standards and conventions.

3.2 Where can I look up unit conversion factors?
-------------------------------------------------

The popular Web search service http://www.google.com/ has a powerful
built-in calculator function and knows a comprehensive set of unit
conversions.

Usage examples:

4 inches
=> 10.16 centimetres

c in furlongs per fortnight
=> the speed of light = 1.8026175 × 10^12 furlongs per fortnight

Another unit converter website:

http://www.convertit.com/Go/ConvertIt/Measurement/Converter.ASP

There is various unit-conversion software available, such as:

http://www.gnu.org/software/units/

A very comprehensive list of conversion factors for units used in the
United States can be found in

Guide for the Use of the International System of Units (SI)
NIST Special Publication 811, 1995 Edition, by Barry N. Taylor.
Appendix B: Conversion Factors
http://physics.nist.gov/Pubs/SP811/

3.3 What is the exact international definition of some non-SI units?
---------------------------------------------------------------------

unit name symbol exact definition

inch in 1 in = 25.4 mm
foot ft 1 ft = 12 in = 0.3048 m
yard yd 1 yd = 3 ft = 0.9144 m
mile 1 mile = 5280 ft = 1609.344 m
nautical mile 1 nautical mile = 1852 m
knot 1 knot = 1.852 km/h
are a 1 a = 100 m²
hectare ha 1 ha = 10000 m²
pint (UK) pt (UK) 1 pt (UK) = 0.56826125 L
gallon (US) gal (US) 1 gal (US) = 231 in³ = 3.785411784 L
pound lb 1 lb = 0.45359237 kg
kilogram force kgf 1 kgf = 9.80665 N
kilopond kp 1 kp = 1 kgf
bar bar 1 bar = 100 kPa
standard atmosphere atm 1 atm = 101.325 kPa
torr Torr 1 Torr = 1/760 atm
technical atmosphere at 1 at = 1 kgf/cm² = 98.0665 kPa
millimetre of water mmH₂O 1 mmH₂O = 10^-4 at = 9.80665 Pa
rad rad 1 rad = 0.01 Gy
rem rem 1 rem = 0.01 Sv
curie Ci 1 Ci = 3.7 × 10^10 Bq
röntgen R 1 R = 2.58 × 10^-4 C/kg

Use of all these non-SI units is deprecated, except for use in fields
where they are still required by law or contract.

[All values and definitions taken from ISO 31:1992 and ISO 1000:1992.]

3.4 What are calories?
-----------------------

One calorie (cal) is the amount of heat required to warm 1 g of
air-free water from 14.5 °C to 15.5 °C at a constant pressure of 1
atm. It is defined as 1 cal = 4.1855 J, but this value has an
uncertainty of 0.5 mJ. There is also an "International Table calorie"
with 1 cal = 4.1868 J, as well as a "thermochemical calorie" with 1
cal = 4.184 J.

In the United States, the kilocalorie (kcal) is often abbreviated as
"Cal".

The kilocalorie is still widely used all over the world to measure the
nutritional energy of food products (usually per 100 g). Perhaps it is
the fact that the term "calories" has become a common synonym for
"nutritional energie" that makes it somewhat difficult for the SI unit
for energy, the joule, to become popular in this area.

("Low-calorie food" may be easier to sell than "low-energy food".)

3.5 What are FFUs and WOMBAT units?
------------------------------------

The collection of units used in the United States lacks a defining
formal name. The term "imperial units" does not quite fit, because
although many of the US units are derived from those of the British
Empire, they are not all identical. Most notably, 1 US pint = 473.1765
mL, whereas 1 Imperial pint = 568.2615 mL. The term "US customary
units" seems to be preferred in government documents.

Two alternative and somewhat less diplomatic names for these units
emerged on the US Metric Association mailing list:

- Flintstone Units or Fred Flintstone Units (FFUs)

- Way Of Measuring Badly in America Today (WOMBAT)
(also: Waste Of Money, Brains And Time)

3.6 Does kilo mean 1024 in computing?
--------------------------------------

Powers of two occur naturally as design dimensions in computer
hardware, in particular for the size of address spaces. It has
therefore become customary in some areas (most notably memory chips)
to use the SI prefixes kilo, mega and giga as if they stood for the
factors 2^10, 2^20 and 2^30 instead of 10^3, 10^6, and 10^9,
respectively. For example, a RAM chip with 65536 bits capacity is
commonly referred to as a "64-kbit-chip".

While such use may be acceptable when it occurs in the names of
product classes (e.g., a "megabit chip" is the smallest chip model
that can contain one million bits), it must not be extended into
formal language, such as parameter tables in product datasheets or
messages generated by software.

The BIPM has clarified that the SI prefixes must unambiguously stand
for the exact powers of ten.

Even in the field of computer design, the prefixes kilo, mega and giga
are very commonly used to refer to powers of ten. For example a 64
kbit communication line transmits exactly 64 000 bits per second and a
200 MHz processor operates with exactly 200 000 000 clock cycles per
second. Bizarre mixtures between binary and decimal interpretations of
the SI prefixes have been spotted in the wild as well. For example,
the 90 mm floppy disk that is sometimes labelled with a capacity of
"1.44 megabytes" has a formatted capacity of 512 × 80 × 18 × 2 = 1.44
× 1000 × 1024 bytes.

In order to help eliminate such abuse of SI prefixes, the
International Electrotechnical Commission in 1999 amended the standard
IEC 27-2 (Letter symbols to be used in electrical technology, Part 2:
Telecommunications and electronics). It now defines new unit prefixes
for powers of two:

1024 = 2^10 = 1 024 kibi Ki
1024^2 = 2^20 = 1 048 576 mebi Mi
1024^3 = 2^30 = 1 073 741 824 gibi Gi
1024^4 = 2^40 = 1 099 511 627 776 tebi Ti
1024^5 = 2^50 = 1 125 899 906 842 624 pebi Pi
1024^6 = 2^60 = 1 152 921 504 606 846 976 exbi Ei

This way, the 90 mm floppy disk has now unambiguously a capacity of
1400 kibibytes (KiB). The standard crystal-oscillator frequency in
wrist watches is 32768 Hz = 32 KiHz.

Note that the symbol for kibi (Ki) starts with an uppercase letter, in
contrast to the symbol for kilo (k).

These new binary prefixes were recently equally defined in IEEE Std
1541-2002 (IEEE trial-use standard for prefixes for binary multiples).

More information:

http://physics.nist.gov/cuu/Units/binary.html
http://www.cofc.edu/~frysingj/binprefixes.html

3.7 What are the official short symbols for bit and byte?
----------------------------------------------------------

The SI does at present not cover units for information. The
conventions in this field are still somewhat less well defined than
they are for SI units. There are some other standards such as IEC 27
that define various computer, telecommunication and psychophysics
units that can be used with the SI. These include bit (bit), byte (B),
neper (Np), shannon (Sh), bel (B), octave, phon, sone, baud (Bd),
erlang (E), and hartley (Hart).

Note: The abbreviation B for byte is slightly problematic for two
reasons. Firstly, the B is also the symbol for the unit bel (used for
the decimal logarithm of the quotient between two power values), but
as the latter is in practice exclusively used with the prefix deci
(decibel = dB), there is little chance of confusion. Secondly, it
breaks the tradition of using an uppercase letter only if the unit was
named after a person.

In French, the unit octet (o) is commonly used instead of byte. In
English, "octet" is commonly used at least in telecommunication
specifications, to unambiguously refer to a group of eight bits.

[There is (was?) also an IEEE standard that says b = bit and B = byte,
but the lowercase b as an abbreviation for bit is far less frequently
used since bit is already meant to be an abbreviation (of "binary
digit").]

3.8 What does the "e" symbol found on many packaged goods mean?
----------------------------------------------------------------

Prepackaged supermarket goods bought in Europe show, next to the
weight or volume indication, a symbol that looks like a slightly large
and bold lowercase letter "e". With this symbol, the manufacturer
guarantees that the tolerance of the indicated weight or volume meets
the requirements of European Union legislation, namely:

Council Directive 75/106/EEC on the approximation of the laws of the
Member States relating to the making-up by volume of certain
prepackaged liquids, 1974-12-19, (Official Journal L 324, 1975-12-16).
http://europa.eu.int/eur-lex/en/consleg/pdf/1975/en_1975L0106_do_001.pdf

Council Directive 76/211/EEC on the approximation of the laws of the
Member States relating to the making-up by weight or by volume
of certain prepackaged products, 1976-01-20, (Official Journal L 046,
1976-02-21, p. 1)
http://europa.eu.int/eur-lex/en/consleg/pdf/1976/en_1976L0211_do_001.pdf

These EU regulations define the maximally allowed negative error of
the packaged content in relation to the label, as well as statistical
tests that manufactured packages must be able to pass.

The exact shape of the "e" is defined, along with various other far
less frequently used symbols, in:

Council Directive 71/316/EEC on the approximation of the laws of the
Member States relating to common provisions for both measuring
instruments and methods of metrological control, 1971-07-26,
(Official Journal L 202, 1971-09-06, p. 1).
http://europa.eu.int/eur-lex/en/consleg/pdf/1971/en_1971L0316_do_001.pdf

The Unicode character set calls this "e" symbol the ESTIMATED SIGN and
encodes it at position U+212E.

Thanks to the many readers of misc.metric-system who provided
suggestions to improve this text.

--
Markus Kuhn, Computer Laboratory, University of Cambridge
http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain

Jim Riley

unread,

May 3, 2004, 6:42:54 PM5/3/04

to

On Sat, 1 May 2004 14:17:04 +0000 (UTC), mg...@cl.cam.ac.uk (Markus
Kuhn) wrote:

>1 Basics
>=========

> The United States lacks a coherent system of units. Economic
> realities, international standards, and the short-comings of the
> inch-pound system (e.g., lack of electrical and chemical units,
> lack of small subunits) force it already to use the metric system
> alongside its customary inch-pound units. American students waste
> at least half a year of math education with developing
> unit-conversion skills (both within the inch-pound system and
> between inch-pound and metric) that are utterly irrelevant in the
> metric-only rest of the world. [The study "Education System
> Benefits of U.S. Metric Conversion", by Richard P. Phelps,
> published in Evaluation Review, February 1996, estimated that
> teaching solely metric measurements could save 82 days of maths

American students do not receive maths [sic] instruction.

> instruction-time annually, worth over 17 billion dollars.]

Does this assume that some of the math and science teachers will be
laid off, or that the school year will be reduced in length (and
salaries decreased accordingly?)

> - Because it dramatically reduces conversion factors in calculations
>
> In spite of a significant amount of secondary school time being
> wasted in the United States in science and math education with
> training the use of conversion factors between the bewildering set
> of units in use there, only few educated Americans know by heart
> how to convert between gallons and cubic feet or inches and miles.

They typically have no need to convert between gallons and cubic feet
unless they have a swimming pool. Do educated Europeans know by heart
how to convert between liters and cubic meters, or do they have to
derive the conversion factor based on knowing that a liter is a cubic
decimeter, or that a milliliter is a cubic centimeter. Likewise,
there is little reason to convert between inches and miles.

> The inch-pound system suffers from a bewildering, random and
> completely unsystematic set of conversion factors between units
> for the same quantity, for instance 1 mile = 1760 yards and 1 US
> gallon = 231 cubic inches.

Why aren't the conversion factors used between different units of time
considering to be bewildering, random, and completely unsystematic?

> - Because metric dimensions are easier to divide by three

> standardized preferred number sequences. For example, in the

> British building industry, it is normal to chose major design
> dimensions (e.g., grid lines on a building plan) as multiples of
> 60 or 600 mm. As a result, common building dimensions can be
> divided by 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 25, 30, 40, 50,
> 60, 75, 100, 120, 150, 200, and 300 without having to resort to
> millimetre fractions. Even without such precautions, it is
> instantly obvious that one kilometre divided three is 333 1/3
> metres and 1/3 L = 333 1/3 mL,

How much of the "wasted" instruction time is spent dealing with mixed
fraction such as are often used with measuring short distances? If
this time was eliminated, would it be instantly obvious that 1/3 L =
333 1/3 mL?

> whereas even inch-pound enthusiasts
> are a bit pressed when asked what 1/3 mile is in yards (answer:
> 586 2/3) or what 1/3 lb is in ounces (5 1/3).

Your claim seems to be based on the notion that people will have
memorized reciprocals. I suspect that it is no easier to determine
what 1/7 of 2.4 km is in m, than it is to determine what 1/7 of 2.4
miles is in yards.

> Furthermore, while
> the use of decimal fractions is preferred in the metric system,
> because this simplifies the mental conversion between different
> units prefixes, there is no reason why vulgar fractions cannot be
> used where it seems appropriate.

Since the use of decimal fractions is preferred, will students receive
training in the use of mixed fractions?

>B) General Physics
>
> Speed of sound: 340 m/s

In air.

> Diameter of solar system: 12 Tm

Is this the major axis of Pluto's orbit?

>E) Temperatures

> Preferred soft drink temperature (US): 0 °C

Says who?

> Typical fridge temperature: 4-8 °C

'fridge' is a shortening of a brand-name of a refrigerator.

> Comfortable office room temperature: 20-25 °C
> (same for swimming-pool water)
>
> Hot day: 25-35 °C
> (same for baby bath water)

How can the temperature for a hot day and a comfortable office be the
same? Is 25°C warm enough for a baby's bath? And is it a good idea
to equivalence "Hot day" and "baby bath water"? To many people,
35°C is not a hot day, but a normal summer day. If someone considers
40°C to be a hot day, do they risk scalding the baby?

> Water boils: 100 °C

(at sea level)

--
Jim Riley

Jukka K. Korpela

unread,

May 4, 2004, 2:17:56 AM5/4/04

to

Jim Riley <jim...@pipeline.com> wrote:

> They typically have no need to convert between gallons and cubic feet
> unless they have a swimming pool.

I have heard that in aquaria groups on Usenet, American aquarium
hobbyists often ask how to compute the volume of an aquarium in gallons
from its dimensions in feet and inches. They usually get a "get metric!"
recommendation. :-) The issue is complicated by the fact that people
often mix US and imperial gallons, especially in Canada.

> Do educated Europeans know by heart
> how to convert between liters and cubic meters,

Yes, that's part of the definition of "educated" these days.

> or do they have to
> derive the conversion factor based on knowing that a liter is a cubic
> decimeter,

Hardly. And strictly speaking, the liter is a non-SI unit approved for
use with the SI, and it is by definition _equivalent_ to the cubic
decimeter.

> or that a milliliter is a cubic centimeter.

It's easy to get confused with such issues. Areas and volumes are
somewhat difficult in the SI, since they unfortunately do not follow the
normal SI rules. But we can live with that.

> Why aren't the conversion factors used between different units of time
> considering to be bewildering, random, and completely unsystematic?

They are. You shouldn't blame the SI for problems with non-SI units,
though. There is only one unit of time in the SI.

> I suspect that it is no easier to determine
> what 1/7 of 2.4 km is in m, than it is to determine what 1/7 of 2.4
> miles is in yards.

The former is a division operation only, unless you count the rewrite of
2.4 km as 2 400 m as an operation. The latter also requires you to
memorize how many yards there are in a mile as well as perform an
additional calculation. Even I - a pure mathematician by education, hence
horrendously poor in numerical calculations - can roughly compute
2 400 / 7 in my mind, at least getting the most significant digit right.
Please don't ask me to do that with the second problem.

>> Speed of sound: 340 m/s
>
> In air.

The idea in the examples is to give a rough idea of the SI units, not to
give instruction on physics. I'm sure that people who need such
information can imply the implicit restriction "under typical
circumstances and interpretation".

>> Diameter of solar system: 12 Tm
>
> Is this the major axis of Pluto's orbit?

It's roughly the average major axis of Pluto's orbit. Here a more precise
formulation might be in order, since there is large variation in what
might be considered as the diameter of the solar system, 12 Tm being the
absolutely smallest possibility. Suggestion:
Average distance of planet Pluto from the Sun: 6 Tm

>> Preferred soft drink temperature (US): 0 °C
>
> Says who?

That sounds odd indeed.

> How can the temperature for a hot day and a comfortable office be the
> same?

Depends on where you live. Might be true in Iceland, if you read "hot" as
"exceptionally hot" and define comfortable office temperature in a modern
healthy way.

> Is 25°C warm enough for a baby's bath? And is it a good idea
> to equivalence "Hot day" and "baby bath water"? To many people,
> 35°C is not a hot day, but a normal summer day.

Where I live, 25 °C is the official limit for hot weather. Temperatures
exceeding it are relatively rare and mostly occur in July only.

I'm pretty sure that even in the US, the expression "hot day" means
different things to different people. It would be odd if it had the same
denotation and connotations in Alaska and in Florida.

Thus, the examples of temperatures are rather problematic and may easily
confuse rather than explain - or they distract by making the reader think
about the vagueness and problems of the examples, rather than the subject
area of SI units.

BTW, I really hope Markus could HTMLify the FAQ, assigning anchors to
subheadings so that we could easily refer - here and elsewhere - to
individual items there. I understand that this might raise the problem of
dual maintenance (plain text and HTML), but these days, I think the HTML
version would suffice, and the FAQ posting could consist e.g. of just a
short announcement of the existence and address and basic topics (e.g.,
top-level table of content, which will change very rarely I presume)
of the FAQ.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Joona I Palaste

unread,

May 4, 2004, 2:24:15 AM5/4/04

to

Jukka K. Korpela <jkor...@cs.tut.fi> scribbled the following:

> Jim Riley <jim...@pipeline.com> wrote:
>> Is 25°C warm enough for a baby's bath? And is it a good idea
>> to equivalence "Hot day" and "baby bath water"? To many people,
>> 35°C is not a hot day, but a normal summer day.

> Where I live, 25 °C is the official limit for hot weather. Temperatures
> exceeding it are relatively rare and mostly occur in July only.

> I'm pretty sure that even in the US, the expression "hot day" means
> different things to different people. It would be odd if it had the same
> denotation and connotations in Alaska and in Florida.

I think even 20 °C is a hot day. 25 °C is scorching(sp?). Do most USAns
view 35 °C as a "normal" day? Would they wear long overcoats, hats and
scarves if they came to Finland in the middle of July, because it's a
freezing 20 °C out there?
And *I* live almost on the extreme southern border of Finland. People
way up there in Utsjoki or Nuorgam (a full 10° latitude more) may think
of even lower temperatures as "hot".

--
/-- Joona Palaste (pal...@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"It's time, it's time, it's time to dump the slime!"
- Dr. Dante

Klaus Wacker

unread,

May 4, 2004, 3:10:06 AM5/4/04

to

Jukka K. Korpela <jkor...@cs.tut.fi> wrote:
[...]

>
> BTW, I really hope Markus could HTMLify the FAQ, assigning anchors to
> subheadings so that we could easily refer - here and elsewhere - to
> individual items there. I understand that this might raise the problem of
> dual maintenance (plain text and HTML), but these days, I think the HTML
> version would suffice, and the FAQ posting could consist e.g. of just a
> short announcement of the existence and address and basic topics (e.g.,
> top-level table of content, which will change very rarely I presume)
> of the FAQ.

Another possibility would be to use something like "lynx -dump" to
produce a text-only version from html automatically.

--
Klaus Wacker wac...@Physik.Uni-Dortmund.DE
Experimentelle Physik V http://www.physik.uni-dortmund.de/~wacker
Universitaet Dortmund Tel.: +49 231 755 3587
D-44221 Dortmund Fax: +49 231 755 4547

Klaus von der Heyde

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May 4, 2004, 3:34:50 AM5/4/04

to

Jukka K. Korpela wrote:

> Areas and volumes are
> somewhat difficult in the SI, since they unfortunately do not follow the
> normal SI rules. But we can live with that.

They follow the SI rules, but these rules are a bit unintuitive
considering the rules of mathematics: the prefixes are prefixes
and not multiplication factors.
1 cm² = 1 (cm)² and not equal to 1 c(m²).

>>> Preferred soft drink temperature (US): 0 °C
>>
>> Says who?
>
> That sounds odd indeed.

Prevents the ice cubes from melting.
By the way, a well-known US soft drink company advertised that its
product to be "most refreshing" at 3 °C in Germany a few years ago.
I wonder if said company calculates its produced volumes in metric,
or if all data from all over the world is converted to cubic miles
or something when reporting to the headquarters... perhaps they
just count the $$$.

Klaus

Klaus von der Heyde

unread,

May 4, 2004, 3:34:52 AM5/4/04

to

Jim Riley wrote:

> Why aren't the conversion factors used between different units of time
> considering to be bewildering, random, and completely unsystematic?

Someone has yet to come up with a reasonable new system that does
not screw up something else. Any timespan can be expressed in
seconds (use prefixes as needed), and scientists are quite happy
with that. So, the only unit of time SI defines is the second.
A "day" has 86400 s, but the time for one revolution of the earth
is not exactly this long[1]. So a new time unit dividing a day in,
say, 1000000 "new seconds" would not be practical.

[1] There are leap seconds to compensate for this.

> Your claim seems to be based on the notion that people will have
> memorized reciprocals. I suspect that it is no easier to determine
> what 1/7 of 2.4 km is in m, than it is to determine what 1/7 of 2.4
> miles is in yards.

It is easier, because it eliminates one multiplication with an
arbitrary conversion factor (how many yards are in one mile?)
There is an implicit multiplication from km to m, but thats only
a shift of the decimal point and therefore easy.
And there are 1000 m to a km, as there are 1000 g to a kg, ...
In the metric world, people would be quite happy with the result
given in km anyway, because they can easily convert to m if they
like, without writing it down or typing it into a calculator.

> Since the use of decimal fractions is preferred, will students receive
> training in the use of mixed fractions?

Yes, this is part of standard math education, at least in Germany.

Klaus

Michael Dahms

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May 4, 2004, 4:32:54 AM5/4/04

to

Jukka K. Korpela wrote:

>
> Jim Riley <jim...@pipeline.com> wrote:
> >
> >> Preferred soft drink temperature (US): 0 °C
> >
> > Says who?
>
> That sounds odd indeed.

Attributing 0 °C to a mixture of ice and water-based liquid sounds like
a good approximation to me.

Michael Dahms

Jukka K. Korpela

unread,

May 4, 2004, 7:00:47 AM5/4/04

to

Michael Dahms <michae...@gkss.de> wrote:

>> >> Preferred soft drink temperature (US): 0 °C
>> >
>> > Says who?
>>
>> That sounds odd indeed.
>
> Attributing 0 °C to a mixture of ice and water-based liquid sounds like
> a good approximation to me.

Then we have a different understanding what "soft drink" means. And even
if you put some ice cubes into your Coke ("soft drink" is just a
Politically Correct name for Coke, right? :-) ), you won't make the
temperature 0 °C or even close. If 0 °C is your preferred temperature for
Coke, you will lose _much_ of the taste. Even more so for tasty drinks.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Jukka K. Korpela

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May 4, 2004, 7:21:22 AM5/4/04

to

Klaus von der Heyde <uzs...@uni-bonn.de> wrote:

> Jukka K. Korpela wrote:
>
>> Areas and volumes are
>> somewhat difficult in the SI, since they unfortunately do not follow
>> the normal SI rules. But we can live with that.
>
> They follow the SI rules, but these rules are a bit unintuitive

I wrote "the normal SI rules" to emphasize the fact that the SI rules for
expressing areas and volumes differ from all the rest. Thet are, of
course, SI rules by definition. Just as it is an SI rule that the unit of
mass is the kilogram, but this still deviates from the _normal_ rule that
the unit does not contain a prefix.

> considering the rules of mathematics: the prefixes are prefixes
> and not multiplication factors.

Pardon? The prefixes are used to express multiples and submultiples, so
surely they are multiplication factors.

> 1 cm² = 1 (cm)² and not equal to 1 c(m²).

The prefix "c" still indicates multiplication by 0.01 - it just applies
to "m", and that's exactly the oddity.

There's no really good way to express areas in SI, unless they are in the
range 0.1 m² to 1000 m². The are and the hectare are not SI units, though
temporarily approved for use with the SI. For large areas we can use km²,
but it's inconvenient for expressing areas like
50 000 m². I hope nobody will suggest the use of dam², even though it
_is_ formally a SI unit (and equivalent to the are), or the use of
hm² (which is equivalent to the hectare).

What we would really need is a normal SI multiple equal to 0.001 m² and
another normal SI multiple equal to 1000 m².

>>>> Preferred soft drink temperature (US): 0 °C
>>>
>>> Says who?
>>
>> That sounds odd indeed.
>
> Prevents the ice cubes from melting.

To prevent ice cubes from melting, keep them in a freezer.

> By the way, a well-known US soft drink company advertised that its
> product to be "most refreshing" at 3 °C in Germany a few years ago.

Rather foolish, but if you wish to achiece that temperature, put your
Coke into a good fridge. Ice cubes are not very good at achieving
specific temperatures, still less maintaining them.

But the basic point is that in a document aimed at promoting the
understanding of the SI worldwide, the examples should be rather free
from cultural dependencies, not to mention matters of taste. For
temperatures, objectively describable things should give enough
possibilities for presenting examples. If some additional info is needed,
then a very small Fahrenheit to Celsius conversion table might be
suitable. You could just tell how much 70 °F is in Celsius degrees, or in
kelvins, instead of characterizing it as cold or warm or typical or
untypical.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Andreas Prilop

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May 4, 2004, 8:36:17 AM5/4/04

to

On Tue, 4 May 2004, Jukka K. Korpela wrote:

> What we would really need is a normal SI multiple equal to 0.001 m² and
> another normal SI multiple equal to 1000 m².

Why?
1000 m² = 31,6 m × 31,6 m
whereas
100 m² = 10 m × 10 m = 1 a
10000 m² = 100 m × 100 m = 1 ha
which looks more suitable to me.

--
Top-posting.
What's the most irritating thing on Usenet?

Gene Nygaard

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May 4, 2004, 9:19:40 AM5/4/04

to

On Tue, 4 May 2004 14:36:17 +0200, Andreas Prilop
<nhtc...@rrzn-user.uni-hannover.de> wrote:

>On Tue, 4 May 2004, Jukka K. Korpela wrote:
>
>> What we would really need is a normal SI multiple equal to 0.001 m² and
>> another normal SI multiple equal to 1000 m².
>
>Why?
> 1000 m² = 31,6 m × 31,6 m
>whereas
> 100 m² = 10 m × 10 m = 1 a
> 10000 m² = 100 m × 100 m = 1 ha
>which looks more suitable to me.

Hardly anybody uses both ares and hectares. Doesn't look more
suitable to me.

Nobody uses any other prefix except "deka" with ares--and in that
case, a name for square meters, to which we could apply the prefix
kilo instead, would work much better, helping get rid of those useless
prefixes which are not powers of 1000.

But the most unsuitable part over all is that we have 1 ha = 1 hm²,
not 1 a = 1 m², an unfathomable, hard to remember offset.
Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

Michael Dahms

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May 4, 2004, 9:33:25 AM5/4/04

to

Jukka K. Korpela wrote:

> And even
> if you put some ice cubes into your Coke ("soft drink" is just a
> Politically Correct name for Coke, right? :-) ), you won't make the
> temperature 0 °C or even close.

Measure it!

Michael Dahms

Andreas Prilop

unread,

May 4, 2004, 9:41:20 AM5/4/04

to

On Tue, 4 May 2004, Gene Nygaard wrote:

>> 1000 m² = 31,6 m × 31,6 m
>> whereas
>> 100 m² = 10 m × 10 m = 1 a
>> 10000 m² = 100 m × 100 m = 1 ha
>> which looks more suitable to me.
>
> Hardly anybody uses both ares and hectares. Doesn't look more
> suitable to me.

Sorry, but you missed my point! Please explain the advantage of
having an area unit that is equal to 31,6 m × 31,6 m instead
of 10 m × 10 m or 100 m × 100 m.

Markus Kuhn

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May 4, 2004, 11:42:41 AM5/4/04

to

"Jukka K. Korpela" <jkor...@cs.tut.fi> writes:

>Jim Riley <jim...@pipeline.com> wrote:
>>> Preferred soft drink temperature (US): 0 °C
>> Says who?
>That sounds odd indeed.

That's how it is commonly served there, with lots of ice cubes,
to keep the drink temperature very close to 0 °C. It is
merely an empirical observation of gastronomical practice in the
US (not taking any effects into account that a sucrose/
fructose solution and some other ingredients may have on the
melting temperature of water ice). The point is that this
is a commonly encountered every-day reference temperature.
I could replace it with "Temperature of an unsalted drink with
lots of ice cubes".

Markus

Jukka K. Korpela

unread,

May 4, 2004, 11:58:11 AM5/4/04

to

Andreas Prilop <nhtc...@rrzn-user.uni-hannover.de> wrote:

> On Tue, 4 May 2004, Jukka K. Korpela wrote:
>
>> What we would really need is a normal SI multiple equal to 0.001 m²
>> and another normal SI multiple equal to 1000 m².
>
> Why?

Because the square meter is the unit of area, and all the usual benefits
of SI prefixes apply. You can conveniently scale all the numbers into the
interval [1, 1000), excluding the case where the value equals zero.

> 1000 m² = 31,6 m × 31,6 m
> whereas
> 100 m² = 10 m × 10 m = 1 a
> 10000 m² = 100 m × 100 m = 1 ha
> which looks more suitable to me.

A square is just a very special case of an area. There's no need to base
the notations on a square, or a circle (which is the most perfect of all
areas, isn't it? :-)). If you wish to visualize, say, 1 k(m²) somehow,
nothing prevents you from thinking about a 10 m × 100 rectangle, or a
20 m × 50 m rectangle.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Jukka K. Korpela

unread,

May 4, 2004, 12:05:52 PM5/4/04

to

Gene Nygaard <gnyg...@nccray.com> wrote:

> Hardly anybody uses both ares and hectares. Doesn't look more
> suitable to me.

Where I live, the hectare is in very common use (e.g., to express areas
of farms), and the are is used too (mostly in contexts like gardening,
I think).

According to EU material I've mentioned earlier, it seems that "deciare"
and "centiare" are used, too, in some countries.

> Nobody uses any other prefix except "deka" with ares

Strange. I've never seen such usage, but I'm not surprised - I hadn't
heard of the centiare before either.

> But the most unsuitable part over all is that we have 1 ha = 1 hm²,
> not 1 a = 1 m², an unfathomable, hard to remember offset.

Indeed. Actually all we need is a special symbol and name for the square
meter (and the cubic meter) and consistent use of SI prefixes for it.
The word "are" would have been quite suitable, but we cannot use it any
more. I wonder if "q" (from Latin "quadrata") could be used.
Unfortunately it could take a gigasecond before such changes could be
agreed on and implemented.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Joona I Palaste

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May 4, 2004, 12:39:00 PM5/4/04

to

Jukka K. Korpela <jkor...@cs.tut.fi> scribbled the following:

> Gene Nygaard <gnyg...@nccray.com> wrote:
>> Hardly anybody uses both ares and hectares. Doesn't look more
>> suitable to me.

> Where I live, the hectare is in very common use (e.g., to express areas
> of farms), and the are is used too (mostly in contexts like gardening,
> I think).

> According to EU material I've mentioned earlier, it seems that "deciare"
> and "centiare" are used, too, in some countries.

Wouldn't a "centiare" be a square metre? Why do we need another name for
that? In Finnish apartments for example, a square metre is called a
square metre.

--
/-- Joona Palaste (pal...@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/

"Normal is what everyone else is, and you're not."
- Dr. Tolian Soran

Sebastian Brocks

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May 4, 2004, 2:15:02 PM5/4/04

to

Gene Nygaard <gnyg...@nccray.com> wrote:

> Hardly anybody uses both ares and hectares. Doesn't look more
> suitable to me.
>

Both are quite common here in Germany, and I've never heard 'decare' before.
--
"Son, a woman is like a beer. They smell good, they look good, you'd step
over your own mother just to get one! But you can't stop at one. You wanna
drink another woman!"
-Homer Simpson

Jim Riley

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May 4, 2004, 4:13:50 PM5/4/04

to

On Tue, 4 May 2004 06:17:56 +0000 (UTC), "Jukka K. Korpela"
<jkor...@cs.tut.fi> wrote:

>Jim Riley <jim...@pipeline.com> wrote:
>
>> They typically have no need to convert between gallons and cubic feet
>> unless they have a swimming pool.
>
>I have heard that in aquaria groups on Usenet, American aquarium
>hobbyists often ask how to compute the volume of an aquarium in gallons
>from its dimensions in feet and inches. They usually get a "get metric!"
>recommendation. :-) The issue is complicated by the fact that people
>often mix US and imperial gallons, especially in Canada.

This is really the same application. The reason that people don't
know how to convert is not because it is a complex calculation, but
because it is an uncommon one. Determining the volume of an aquarium
in cubic inches is no more difficult than determining its volume in
cubic meters. It might even be easier given the chance of a misplaced
decimal point in the metric application.

>> Do educated Europeans know by heart
>> how to convert between liters and cubic meters,
>
>Yes, that's part of the definition of "educated" these days.

It seems like a magic number to remember, useful only when computing
the volume of swimming pools and aquariums.

>> or do they have to
>> derive the conversion factor based on knowing that a liter is a cubic
>> decimeter,
>
>Hardly. And strictly speaking, the liter is a non-SI unit approved for
>use with the SI, and it is by definition _equivalent_ to the cubic
>decimeter.

This would seem to make it more likely that people would not know by
heart the number of liters in a cubic meter.

>> or that a milliliter is a cubic centimeter.
>
>It's easy to get confused with such issues. Areas and volumes are
>somewhat difficult in the SI, since they unfortunately do not follow the
>normal SI rules. But we can live with that.
>
>> Why aren't the conversion factors used between different units of time
>> considering to be bewildering, random, and completely unsystematic?
>
>They are. You shouldn't blame the SI for problems with non-SI units,
>though. There is only one unit of time in the SI.

Isn't this saying that SI is not practical for everyday use?

>> I suspect that it is no easier to determine
>> what 1/7 of 2.4 km is in m, than it is to determine what 1/7 of 2.4
>> miles is in yards.
>
>The former is a division operation only, unless you count the rewrite of
>2.4 km as 2 400 m as an operation. The latter also requires you to
>memorize how many yards there are in a mile as well as perform an
>additional calculation. Even I - a pure mathematician by education, hence
>horrendously poor in numerical calculations - can roughly compute
>2 400 / 7 in my mind, at least getting the most significant digit right.
>Please don't ask me to do that with the second problem.

If you are doing it in your head, there is always the risk of dividing
by 7 first, and then misplacing the decimal point. If you were using
a calculator, you would only have to know the conversion factor.

>>> Speed of sound: 340 m/s
>>
>> In air.
>
>The idea in the examples is to give a rough idea of the SI units, not to
>give instruction on physics.

340 m/s is an extremely poor value for the speed of sound in water.

> I'm sure that people who need such
>information can imply the implicit restriction "under typical
>circumstances and interpretation".
>
>>> Diameter of solar system: 12 Tm
>>
>> Is this the major axis of Pluto's orbit?
>
>It's roughly the average major axis of Pluto's orbit. Here a more precise
>formulation might be in order, since there is large variation in what
>might be considered as the diameter of the solar system, 12 Tm being the
>absolutely smallest possibility. Suggestion:
> Average distance of planet Pluto from the Sun: 6 Tm

>>> Preferred soft drink temperature (US): 0 °C
>>
>> Says who?
>
>That sounds odd indeed.
>
>> How can the temperature for a hot day and a comfortable office be the
>> same?
>
>Depends on where you live. Might be true in Iceland, if you read "hot" as
>"exceptionally hot" and define comfortable office temperature in a modern
>healthy way.
>
>> Is 25°C warm enough for a baby's bath? And is it a good idea
>> to equivalence "Hot day" and "baby bath water"? To many people,
>> 35°C is not a hot day, but a normal summer day.
>
>Where I live, 25 °C is the official limit for hot weather. Temperatures
>exceeding it are relatively rare and mostly occur in July only.

It was a coolish 23°C where I live yesterday, followed by an overnight
low that was within two degrees of the record low for the date.

>I'm pretty sure that even in the US, the expression "hot day" means
>different things to different people. It would be odd if it had the same
>denotation and connotations in Alaska and in Florida.
>
>Thus, the examples of temperatures are rather problematic and may easily
>confuse rather than explain - or they distract by making the reader think
>about the vagueness and problems of the examples, rather than the subject
>area of SI units.
>
>BTW, I really hope Markus could HTMLify the FAQ, assigning anchors to
>subheadings so that we could easily refer - here and elsewhere - to
>individual items there. I understand that this might raise the problem of
>dual maintenance (plain text and HTML), but these days, I think the HTML
>version would suffice, and the FAQ posting could consist e.g. of just a
>short announcement of the existence and address and basic topics (e.g.,
>top-level table of content, which will change very rarely I presume)
>of the FAQ.

--
Jim Riley

Jim Riley

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May 4, 2004, 4:38:20 PM5/4/04

to

On 4 May 2004 06:24:15 GMT, Joona I Palaste <pal...@cc.helsinki.fi>
wrote:

>Jukka K. Korpela <jkor...@cs.tut.fi> scribbled the following:
>> Jim Riley <jim...@pipeline.com> wrote:
>>> Is 25°C warm enough for a baby's bath? And is it a good idea
>>> to equivalence "Hot day" and "baby bath water"? To many people,
>>> 35°C is not a hot day, but a normal summer day.
>
>> Where I live, 25 °C is the official limit for hot weather. Temperatures
>> exceeding it are relatively rare and mostly occur in July only.
>
>> I'm pretty sure that even in the US, the expression "hot day" means
>> different things to different people. It would be odd if it had the same
>> denotation and connotations in Alaska and in Florida.
>
>I think even 20 °C is a hot day. 25 °C is scorching(sp?). Do most USAns
>view 35 °C as a "normal" day?

I suspect that for most people in the world, 5% of the days have a
high temperature at or above 35°C.

> Would they wear long overcoats, hats and
>scarves if they came to Finland in the middle of July, because it's a
>freezing 20 °C out there?

Hypothermia is not something to joke about.

>And *I* live almost on the extreme southern border of Finland. People
>way up there in Utsjoki or Nuorgam (a full 10° latitude more) may think
>of even lower temperatures as "hot".

Finland is the second most northern country in the world (measured by
its southernmost extremity).

--
Jim Riley

Jukka K. Korpela

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May 4, 2004, 4:48:59 PM5/4/04

to

Joona I Palaste <pal...@cc.helsinki.fi> wrote:

> Wouldn't a "centiare" be a square metre?

Yes.

> Why do we need another name for that?

We would need a name for the square metre in order to be able to say
things more compactly and, more importantly, to form multiples and
submultiples as for other SI units.

But "centiare" is inadequate of course, since it's a multiple of a non-SI
unit. It is used, however, as Google hits indicate; it often appears in
the form "centare".

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Jukka K. Korpela

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May 4, 2004, 5:01:39 PM5/4/04

to

Jim Riley <jim...@pipeline.com> wrote:

> This is really the same application.

Well, aquaria are swimming pools for the fish, at least potentially
(though there are plant aquaria too). But it seems that you will explain
any volume as a swimming pool.

> The reason that people don't
> know how to convert is not because it is a complex calculation, but
> because it is an uncommon one.

There's nothing uncommon about it. Aquarium hobbyists calculate such
things often, and they still have problems with it, when they use Anglo-
Saxon units.

> Determining the volume of an aquarium
> in cubic inches is no more difficult than determining its volume in
> cubic meters.

It depends on the data you have, but in any case, you would have just the
cubic inches, and you need some flavor of gallons.

> It might even be easier given the chance of a
> misplaced decimal point in the metric application.

Are you trolling, or just trying to be funny?

> It seems like a magic number to remember, useful only when computing
> the volume of swimming pools and aquariums.

The number 1 000 is really magic - it's used throughout the SI, and
elsewhere too.

>>They are. You shouldn't blame the SI for problems with non-SI units,
>>though. There is only one unit of time in the SI.
>
> Isn't this saying that SI is not practical for everyday use?

No, the SI is practical, old units aren't, but they are tolerated, for
the time being, due to their widespread use.

> If you are doing it in your head, there is always the risk of
> dividing by 7 first, and then misplacing the decimal point. If you
> were using a calculator, you would only have to know the conversion
> factor.

And to type the digits correctly. But when the SI is used, there is no
need to memorize conversion factors in either case.

>>The idea in the examples is to give a rough idea of the SI units, not
>>to give instruction on physics.
>
> 340 m/s is an extremely poor value for the speed of sound in water.

OK, it seems you were just trolling. I hope you didn't enjoy.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Alexander Becher

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May 4, 2004, 5:04:04 PM5/4/04

to

Jim Riley wrote:
>>> Do educated Europeans know by heart
>>> how to convert between liters and cubic meters,
>>
>>Yes, that's part of the definition of "educated" these days.
>
>It seems like a magic number to remember, useful only when computing
>the volume of swimming pools and aquariums.

As I understand it, 1000 is the _only_ magic number in the metric
system (if we do not attribute magic to the number 1). Multiplication
and division by it is easily done by right or left shifting the decimal
point by three digits.

>>> or do they have to
>>> derive the conversion factor based on knowing that a liter is a cubic
>>> decimeter,
>>
>>Hardly. And strictly speaking, the liter is a non-SI unit approved for
>>use with the SI, and it is by definition _equivalent_ to the cubic
>>decimeter.
>
>This would seem to make it more likely that people would not know by
>heart the number of liters in a cubic meter.

I have to confess that I didn't. It took me five seconds to remember,
using a bit of visualization.

Alexander
--
PGP key available

Jim Riley

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May 4, 2004, 5:29:15 PM5/4/04

to

On Tue, 04 May 2004 09:34:52 +0200, Klaus von der Heyde
<uzs...@uni-bonn.de> wrote:

>Jim Riley wrote:
>
>> Why aren't the conversion factors used between different units of time
>> considering to be bewildering, random, and completely unsystematic?
>
>Someone has yet to come up with a reasonable new system that does
>not screw up something else. Any timespan can be expressed in
>seconds (use prefixes as needed), and scientists are quite happy
>with that.

Yet even in the FAQ, two measurements that are of comparable magnitude
(speed of sound and cruising speed of passenger airplanes) a different
time interval was used. I had to calculate whether the range for the
airplanes included supersonic flight or not.

> So, the only unit of time SI defines is the second.
>A "day" has 86400 s, but the time for one revolution of the earth
>is not exactly this long[1]. So a new time unit dividing a day in,
>say, 1000000 "new seconds" would not be practical.
>
>[1] There are leap seconds to compensate for this.
>
>> Your claim seems to be based on the notion that people will have
>> memorized reciprocals. I suspect that it is no easier to determine
>> what 1/7 of 2.4 km is in m, than it is to determine what 1/7 of 2.4
>> miles is in yards.
>
>It is easier, because it eliminates one multiplication with an
>arbitrary conversion factor (how many yards are in one mile?)

5280 feet in a mile, 3 feet in a yard, 440 yards in a quarter mile.

>There is an implicit multiplication from km to m, but thats only
>a shift of the decimal point and therefore easy.

It requires adding digits first.

>And there are 1000 m to a km, as there are 1000 g to a kg, ...
>In the metric world, people would be quite happy with the result
>given in km anyway, because they can easily convert to m if they
>like, without writing it down or typing it into a calculator.

Most people would be content with leaving 1/7 of 2.4 miles expressed
in miles as well. The complexity in the FAQ was an artificial
problem.

>> Since the use of decimal fractions is preferred, will students receive
>> training in the use of mixed fractions?
>
>Yes, this is part of standard math education, at least in Germany.

Does this have practical application?

--
Jim Riley

Michael Dahms

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May 5, 2004, 1:27:39 AM5/5/04

to

Jukka K. Korpela wrote:

> But "centiare" is inadequate of course, since it's a multiple of a non-SI
> unit. It is used, however, as Google hits indicate; it often appears in
> the form "centare".

Where is it really used? I didn't find anything relevant using Google.

Michael Dahms

Jukka K. Korpela

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May 5, 2004, 5:09:35 AM5/5/04

to

Michael Dahms <michae...@gkss.de> wrote:

>> But "centiare" is inadequate of course, since it's a multiple of a
>> non-SI unit. It is used, however, as Google hits indicate; it often
>> appears in the form "centare".
>
> Where is it really used? I didn't find anything relevant using
> Google.

I found quite a many hits. Examples:

"Bicherée de Lyon (196 toises carrées lyonnaises) : 12 ares, 93
centiares"
(in the context of explaining old units in metric terms!)

"10 ares 22 centiares"
(in an official document dated 2001)

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Esa A E Peuha

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May 5, 2004, 5:12:52 AM5/5/04

to

Jim Riley <jim...@pipeline.com> writes:

> Finland is the second most northern country in the world (measured by
> its southernmost extremity).

So what? Alaska is as far north as Finland but colder on average (much
colder in winter, not so much so in summer).

--
Esa Peuha
student of mathematics at the University of Helsinki
http://www.helsinki.fi/~peuha/

Joona I Palaste

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May 5, 2004, 6:29:56 AM5/5/04

to

Esa A E Peuha <esa....@helsinki.fi> scribbled the following:

> Jim Riley <jim...@pipeline.com> writes:
>> Finland is the second most northern country in the world (measured by
>> its southernmost extremity).

> So what? Alaska is as far north as Finland but colder on average (much
> colder in winter, not so much so in summer).

And if we go by how many countries reach further north than Finland, we
end up with quite a lot more than one or two.
Let's see: Norway, Russia, Canada, the USA, even Denmark.
But I suppose those countries are warm and fuzzy all over, because they
also reach further south than Finland?

--
/-- Joona Palaste (pal...@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/

"It's not survival of the fattest, it's survival of the fittest."
- Ludvig von Drake

Christoph Paeper

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May 5, 2004, 2:13:12 PM5/5/04

to

*Sebastian Brocks* <sebe-...@gmx.net>:

> Gene Nygaard <gnyg...@nccray.com> wrote:
>
>> Hardly anybody uses both ares and hectares.
>

> Both are quite common here in Germany,

The most common unit of area in German media is the "Fußballfeld" (soccer
field). Sadly. Also pressure is often given in "Tonnen".

> and I've never heard 'decare' before.

Me neither, but it isn't hard to figure its meaning and convert it unlike
"acre" or "township".
My father, a farmer, hops between Zentner/Morgen (50 kg/0.25 ha = 0.02
kg/m²) and Dezitonne/Hektar (1 dt/ha = 10 t/km² = 0.01 kg/m²) even inside
one sentence, but never uses Ar (are) nor fractions thereof.

--
Reality is an illusion that occurs due to the lack of alcohol.

Jim Riley

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May 5, 2004, 5:37:30 PM5/5/04

to

On 05 May 2004 12:12:52 +0300, Esa A E Peuha <esa....@helsinki.fi>
wrote:

>Jim Riley <jim...@pipeline.com> writes:
>
>> Finland is the second most northern country in the world (measured by
>> its southernmost extremity).
>
>So what? Alaska is as far north as Finland but colder on average (much
>colder in winter, not so much so in summer).

Few people live in Finland or Alaska. Their experience is atypical
for most of the world.

--
Jim Riley

Jim Riley

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May 5, 2004, 5:59:05 PM5/5/04

to

On Tue, 4 May 2004 15:41:20 +0200, Andreas Prilop
<nhtc...@rrzn-user.uni-hannover.de> wrote:

>Sorry, but you missed my point! Please explain the advantage of
>having an area unit that is equal to 31,6 m × 31,6 m instead
>of 10 m × 10 m or 100 m × 100 m.

There is not a particular advantage to any of these. If you own a lot
that is 1000 square meters, it could be nearly square, or deep and
narrow (20 m by 50 m), or moderately deep (25 m by 40 m).

If your lot was 25 m by 40 m, it would be impossible to tile it with
10 are-sized squares. This leaves you stuck with computing the area
(height times width) and having either memorized or needing to look up
the number of square meters in an are.

--
Jim Riley

Christoph Paeper

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May 5, 2004, 6:40:24 PM5/5/04

to

*Jim Riley* <jim...@pipeline.com>:

>
> having either memorized or needing to look up
> the number of square meters in an are.

I believe everyone using are and hectare knows, that they form a factor 100
series starting with square meter and ending with square kilometer.

--
Every rose has its ş.

Jim Riley

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May 5, 2004, 8:32:23 PM5/5/04

to

On Tue, 4 May 2004 21:01:39 +0000 (UTC), "Jukka K. Korpela"
<jkor...@cs.tut.fi> wrote:

>Jim Riley <jim...@pipeline.com> wrote:
>
>> This is really the same application.
>
>Well, aquaria are swimming pools for the fish, at least potentially
>(though there are plant aquaria too). But it seems that you will explain
>any volume as a swimming pool.
>
>> The reason that people don't
>> know how to convert is not because it is a complex calculation, but
>> because it is an uncommon one.
>
>There's nothing uncommon about it. Aquarium hobbyists calculate such
>things often, and they still have problems with it, when they use Anglo-
>Saxon units.

Aquarium hobbyists are uncommon. If they have a number of tanks, they
would know the volume by looking at it, and not need to calculate it
from its dimensions. If they have a few tanks, then then it is
unusual for them to compute it.

>> Determining the volume of an aquarium
>> in cubic inches is no more difficult than determining its volume in
>> cubic meters.
>
>It depends on the data you have, but in any case, you would have just the
>cubic inches, and you need some flavor of gallons.
>
>> It might even be easier given the chance of a
>> misplaced decimal point in the metric application.
>
>Are you trolling, or just trying to be funny?

If you are doing it in your head it may be. Say you have a tank that
is .3 by .3 by .4. 3 times 3 times 4 is 24. They then realize that
it is not 24, so you guess maybe that it is .24, and then add a zero
so that they can convert to liters. They then say that they have a
240 liter tank, and the fish store sells them too big of a pump and to
many fish.

>> It seems like a magic number to remember, useful only when computing
>> the volume of swimming pools and aquariums.
>
>The number 1 000 is really magic - it's used throughout the SI, and
>elsewhere too.

How many square meters in an are?

>>>They are. You shouldn't blame the SI for problems with non-SI units,
>>>though. There is only one unit of time in the SI.
>>
>> Isn't this saying that SI is not practical for everyday use?
>
>No, the SI is practical, old units aren't, but they are tolerated, for
>the time being, due to their widespread use.

Then why should the US switch to SI?

>> If you are doing it in your head, there is always the risk of
>> dividing by 7 first, and then misplacing the decimal point. If you
>> were using a calculator, you would only have to know the conversion
>> factor.
>
>And to type the digits correctly. But when the SI is used, there is no
>need to memorize conversion factors in either case.

Is this any different than memorizing the value of pi, or e, or the
distance to the Sun, or the circumference of the Earth?

--
Jim Riley

DWT

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May 6, 2004, 12:50:52 AM5/6/04

to

jim...@pipeline.com wrote in
<Jsdmc.6394$a47....@newsread3.news.atl.earthlink.net>:

| If your lot was 25 m by 40 m, it would be impossible to tile it with
| 10 are-sized squares.

You could if you cut two of them in half. Even the halves would be unwieldy,
though. I wouldn't want to try carrying one.

--
David W. Tamkin

The reply address will be invalid after midnight US Central Time on 12May2004
unless tiled with are-sized squares.

Michael Dahms

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May 6, 2004, 1:49:13 AM5/6/04

to

Jukka K. Korpela wrote:

> "10 ares 22 centiares"
> (in an official document dated 2001)

Thanks. Seems to be a french speciality. In Germany 1022 m^2 is
generally used.

Michael Dahms

Klaus von der Heyde

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May 6, 2004, 2:55:47 AM5/6/04

to

Jim Riley wrote:

> If you are doing it in your head it may be. Say you have a tank that
> is .3 by .3 by .4.

Is that 0.3 m by 0.3 m by 0.4 m?

> 3 times 3 times 4 is 24.

So, you want to calculate in decimetres, so:
3 dm * 3 dm * 4 dm = 36 dm³ = 36 l,
one of the most easy examples. The metric system allows you to shift
the comma before caclulation, too (if you have problems to calculate
0 3 * 0.3 * 0.4 = 0.036), and as it happens, dm is just fine here to
get the litre figure we want.

> They then realize that it is not 24,

It is something with 36, yes :)

> so you guess maybe that it is .24, and then add a zero
> so that they can convert to liters. They then say that they have a
> 240 liter tank, and the fish store sells them too big of a pump and to
> many fish.

The mistake you present here would only happen to someone completely
unaccustomed to the metric system.

>>No, the SI is practical, old units aren't, but they are tolerated, for
>>the time being, due to their widespread use.
>
> Then why should the US switch to SI?

To get a well-designed, practical and proven system of units for
distances (including areas and volumes), masses etc. at least.

> Is this any different than memorizing the value of pi, or e, or the
> distance to the Sun, or the circumference of the Earth?

Keep it simple. Use conversion factors only when necessary.
I always wonder why USians do not use in³ or ft³ for volumes, but
gallons, requiring an additional conversion factor (it is an
integer, at least: 231 in³, I had to look this up somewhere).

Klaus

Jukka K. Korpela

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May 6, 2004, 11:54:26 AM5/6/04

to

Jim Riley <jim...@pipeline.com> wrote:

> Aquarium hobbyists are uncommon.

You don't know the actual figures, do you?

I would expect to find more people with an aquarium than with a swimming
pool, actually. Anyway, your original claim that people "typically have

no need to convert between gallons and cubic feet unless they have a

swimming pool" has apparently been disproved, or justly ridiculed, but
it's a common feature in trolls to quickly move to other issues after
such occasions.

> If they have a number of tanks, they
> would know the volume by looking at it, and not need to calculate it
> from its dimensions. If they have a few tanks, then then it is
> unusual for them to compute it.

You don't know much about the aquarium hobby either, do you? You seem to
be more familiar with trolling.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Christoph Paeper

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May 6, 2004, 12:54:01 PM5/6/04

to

*Klaus von der Heyde* <uzs...@uni-bonn.de>:

> Jim Riley wrote:
>
>> Say you have a tank that is .3 by .3 by .4.
>
> Is that 0.3 m by 0.3 m by 0.4 m?

Or if one prefers 3/10 m by 3/10 m by 4/10 m. That is for 5th-graders:
(3×3×4)/(10×10×10) m×m×m
= 36/10³ m³ [= 36/1000 m³]
= 36 × 1/10³ m³
= 36 (1/10 m)³
= 36 dm³
= 36 l.

>> Then why should the US switch to SI?

To save money and earn more.

> I always wonder why USians do not use in³ or ft³ for volumes,

Well, at least a register ton is 100 cubic feet. (It seems they like to
write it out just like on street signs.)
Quick, how many cubic inches are there in one cubic foot? Hint: one foot is
twelve inches.

> but gallons, requiring an additional conversion factor

At least they have given up using several different gallons centuries ago.
Except for liquid and dry (268.8 in³) measurement of course.

> (it is an integer, at least: 231 in³, I had to look this up somewhere).

277.42 in³ for liquid and dry in the UK, though. (Times 0.254^3 to get
liters.)

Madness.

--
The Hitchhiker's Guide to the Galaxy:
"In the beginning the Universe was created.
This has made a lot of people very angry
and been widely regarded as a bad move."

Do not answer

unread,

May 6, 2004, 3:12:02 PM5/6/04

to

Klaus von der Heyde wrote:
> Jim Riley wrote:
>
>
>>If you are doing it in your head it may be. Say you have a tank that
>>is .3 by .3 by .4.
>
>
> Is that 0.3 m by 0.3 m by 0.4 m?
>
>
>>3 times 3 times 4 is 24.
>
>
> So, you want to calculate in decimetres, so:
> 3 dm * 3 dm * 4 dm = 36 dm³ = 36 l,
> one of the most easy examples. The metric system allows you to shift
> the comma before caclulation, too (if you have problems to calculate
> 0 3 * 0.3 * 0.4 = 0.036), and as it happens, dm is just fine here to
> get the litre figure we want.

Yes! This is the way to do it!
3 x 3 x 4 = 36 and since it was dm you used and you learned
in school that dm3 = l the calculation is easy.

And wouldn't YOU see the difference between a tank that was
7.9 gallons (or would that be 7 gallons, 4 quarts and 2 pints
or somesuch?) and one that was 79 gallons?

Asbjorn
--
To reach me by e-mail, please use _sheridan at babcon dot org_.

Jim Riley

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May 6, 2004, 6:19:16 PM5/6/04

to

How did they come to know this?

--
Jim Riley

Jim Riley

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May 6, 2004, 8:19:31 PM5/6/04

to

On Thu, 06 May 2004 08:55:47 +0200, Klaus von der Heyde
<uzs...@uni-bonn.de> wrote:

>Jim Riley wrote:
>
>> If you are doing it in your head it may be. Say you have a tank that
>> is .3 by .3 by .4.
>
>Is that 0.3 m by 0.3 m by 0.4 m?

If you are doing this in your head, would you add the units? You
either just measured your tank or estimated its dimensions.

>> 3 times 3 times 4 is 24.
>
>So, you want to calculate in decimetres, so:

Why do I want to calculate in decimeters? I know that the volume of a
rectangular solid is the product of width times depth times height.
Who measures things in decimeters? People on this group are condemned
for using centimeters.

>3 dm * 3 dm * 4 dm = 36 dmł = 36 l,

>one of the most easy examples. The metric system allows you to shift
>the comma before caclulation, too (if you have problems to calculate
>0 3 * 0.3 * 0.4 = 0.036), and as it happens, dm is just fine here to
>get the litre figure we want.
>
>> They then realize that it is not 24,
>
>It is something with 36, yes :)

I shouldn't have changed the dimensions of my aquarium after I chose
the mistake I was going to make.

>> so you guess maybe that it is .24, and then add a zero
>> so that they can convert to liters. They then say that they have a
>> 240 liter tank, and the fish store sells them too big of a pump and to
>> many fish.
>
>The mistake you present here would only happen to someone completely
>unaccustomed to the metric system.

>>>No, the SI is practical, old units aren't, but they are tolerated, for
>>>the time being, due to their widespread use.
>>
>> Then why should the US switch to SI?
>
>To get a well-designed, practical and proven system of units for
>distances (including areas and volumes), masses etc. at least.

How is the system for measuring time well-designed or practical?

>> Is this any different than memorizing the value of pi, or e, or the
>> distance to the Sun, or the circumference of the Earth?
>
>Keep it simple. Use conversion factors only when necessary.

>I always wonder why USians do not use inł or ftł for volumes, but

>gallons, requiring an additional conversion factor (it is an

>integer, at least: 231 inł, I had to look this up somewhere).

It depends on the application. The capacity of a refrigerator would
be measured in cubic feet, a gas tank in gallons.

There is really no reason to remember the conversion factor between
gallons and square feet or square inches. I had no idea that it was
an exact amount, and would have had to look it up somewhere.

--
Jim Riley

Jim Riley

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May 6, 2004, 8:46:28 PM5/6/04

to

On Thu, 6 May 2004 18:54:01 +0200, Christoph Paeper
<christop...@nurfuerspam.de> wrote:

>*Klaus von der Heyde* <uzs...@uni-bonn.de>:
>> Jim Riley wrote:
>>
>>> Say you have a tank that is .3 by .3 by .4.
>>
>> Is that 0.3 m by 0.3 m by 0.4 m?
>
>Or if one prefers 3/10 m by 3/10 m by 4/10 m. That is for 5th-graders:

I just re-measured it: is 35 cm by 32 cm by 44 cm.

> (3×3×4)/(10×10×10) m×m×m
> = 36/10³ m³ [= 36/1000 m³]
> = 36 × 1/10³ m³
> = 36 (1/10 m)³
> = 36 dm³
> = 36 l.
>
>>> Then why should the US switch to SI?
>
>To save money and earn more.

How much would I save if I didn't have to use factors of 60 and 24 for
measuring time?

>> I always wonder why USians do not use in³ or ft³ for volumes,
>
>Well, at least a register ton is 100 cubic feet. (It seems they like to
>write it out just like on street signs.)

What is a "register ton"? What do you mean by "write it out just like
on street sign"? Do you mean like writing "Road", "Street", "Aveneue"
and "Boulevard" brather than "RD", "ST", "AVE", and "BLVD"?

>Quick, how many cubic inches are there in one cubic foot? Hint: one foot is
>twelve inches.

How many cubic centimeters in a cube that is 12 centimeters on a side?

--
Jim Riley

Jim Riley

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May 6, 2004, 10:51:13 PM5/6/04

to

On Thu, 6 May 2004 15:54:26 +0000 (UTC), "Jukka K. Korpela"
<jkor...@cs.tut.fi> wrote:

>Jim Riley <jim...@pipeline.com> wrote:
>
>> Aquarium hobbyists are uncommon.
>
>You don't know the actual figures, do you?

But I can look it up.

According to a survey by the American Pet Products Manufacturers
Association (APPMA), 12.9% of households in the US own fish. I
suspect the vast majority of these are goldfish bowls.

http://hmsc.oregonstate.edu/projects/msap/PS/ornamentals.html

According to a survey for the National Pool and Spa Institute, 8% of
households have a swimming pool.

http://www.pkdata.net/PKData/Waveline/5/Waveline5.htm

>I would expect to find more people with an aquarium than with a swimming
>pool, actually.

It appears that in the United States, owners of swimming pools and
aquariums are in comparable numbers. The second site above has some
regional information that might explain why someone from Finland,
albeit the far southern part, might not expect this.

> Anyway, your original claim that people "typically have
>no need to convert between gallons and cubic feet unless they have a

>swimming pool" has apparently been disproved.

Americans typically have no need to convert between cubic feet and
gallons. This is a true statement, and explains why most Americans
don't know how to convert between cubic feet and gallons. It is not
that they don't know how to do the donversion, but they have no reason
to do it, and no reason to remember the conversion factor.

I gave one application to emphasize how atypical it is. That you can
give another atypical application does not make it typical. And of
course an aquarist or swimming pool owner need not know how to convert
in order to be successful. It's not like someone will sink or swim
based on their ability to do the conversion. Perhaps you have trolls
and witches mixed up. Even if they do the conversion, they might not
do it often enough to remember that a 3 ft x 7 ft x 11 ft pool
contains 1728 gallons.

>> If they have a number of tanks, they
>> would know the volume by looking at it, and not need to calculate it
>> from its dimensions. If they have a few tanks, then then it is
>> unusual for them to compute it.
>
>You don't know much about the aquarium hobby either, do you?

How often would you have to calculate the volume of a tank? It's not
like it changes from day to day.

--
Jim Riley

Jim Riley

unread,

May 6, 2004, 11:01:18 PM5/6/04

to

On Thu, 06 May 2004 08:55:47 +0200, Klaus von der Heyde
<uzs...@uni-bonn.de> wrote:

>Keep it simple. Use conversion factors only when necessary.

>I always wonder why USians do not use inł or ftł for volumes, but

>gallons, requiring an additional conversion factor (it is an

>integer, at least: 231 inł, I had to look this up somewhere).

Just remember that it factors into 3 x 7 x 11 (3 of the 5 smallest
primes, leaving out the two used for the metric system 2 and 5).

--
Jim Riley

Jukka K. Korpela

unread,

May 7, 2004, 1:30:19 AM5/7/04

to

Jim Riley <jim...@pipeline.com> wrote:

>>You don't know the actual figures, do you?
>
> But I can look it up.
>
> According to a survey by the American Pet Products Manufacturers
> Association (APPMA), 12.9% of households in the US own fish. I
> suspect the vast majority of these are goldfish bowls.

So you looked up something that confirmed that your previous statement
was just wrong, and you immediately make up an assumption that you then
use to refute what you just found.

Besides, you are just trying to obscure the basic issue that there _are_
people who need to calculate volumes from dimensions. You gave an example
(swimming pools) "to emphasize how atypical it is", and now you're
yourself saying it applies to 8 % (that means millions of people in the
US) _and_ you will try to explain away all other examples, even if they
are even more common.

If you add up several cases that apply to 8 % or 13 % people, you will
soon end up with impressive figures, even if the sets are not disjoint
(meaning that some people may have need for the calculations for
_several_ reasons).

So you are just a clumsy troll. We would have some use for a well-
argumenting opponent, but there's nothing we can use you for but as a
killfile filler.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Christoph Paeper

unread,

May 6, 2004, 8:50:44 PM5/6/04

to

*Jim Riley* <jim...@pipeline.com>:

> On Thu, 6 May 2004 00:40:24 +0200, Christoph Paeper
>

>> I believe everyone using are and hectare knows, that they form a factor
>> 100 series starting with square meter and ending with square kilometer.
>
> How did they come to know this?

How did you come to know the factors between inch, foot and yard? Are and
hectare just have much simpler factors, although not really in compliance
with SI's standard 10訟dimension.

--
"Show me a sane man and I will cure him." -- C.G. Jung

Paul Stoffers

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May 7, 2004, 7:06:20 AM5/7/04

to

"Jim Riley" <jim...@pipeline.com> schreef in bericht
news:rIfmc.6503$a47....@newsread3.news.atl.earthlink.net

[snip aquarium discussion]

>
> Then why should the US switch to SI?
>

There's one reason that hasn't been mentioned yet, to my surprise: trade, or
more in general: communication. I wouldn't have any trouble making a dish
using a recipe with ounces and pints, *if I had scales and a measuring cup
indicating those units*, but I don't. I also do not see the difference in
setting a Celsius temperature on an oven with a Celsius scale, or doing the
same with a "Fahrenheit" oven, but *I* only have an oven with Celsius
indication. I do not intend to have two sets of kitchen utensils.

A US car manufacturer can use non-metric nuts and bolts, but it means that
(e.g.) European (amateur) mechanics should have two sets of spanners, both
metric and non-metric. On the other hand US mechanics might want to tinker
with European cars, so they as well need two sets of wrenches. Ofcourse the
car manufacturers could decide on using the nuts and bolts according to
market, but that would require more elaborate stock management.

The manufacturers of scales, measuring cups, tape measures, ovens (etc.) are
faced with a similar problem. Either make two different products, US-type
and "rest-of-the world"-type, or one product with both units. (Actually I do
have a tape measure with both inches/feet and cm.) Either way it costs
money.

Labeling is another issue. Sometimes a specific unit is required, sometimes
the use of any other unit is prohibited. If using both units on the label is
allowed, the label gets cramped with information and errors are more likely
to occur. Again, if only one type of unit were used, it would save money and
time.

Standardization is beneficial to world business, both for consumers and
companies. It might even contribute to world peace as it increases mutual
understanding. Using the same units is the first step towards
standardization. Since most of the world already uses the metric system it's
more obvious for the US to convert to the metric system than the other way
round.

The US should switch to SI:
- /not/ because SI is supposedly "better" than inch/pound/pint (although I
think it is),
- /not/ because "we" are consistent in using SI units (we are not)

but for the simple reason it's unavoideble if "you" still want to buy goods
from, or sell goods to, the rest of the world.

Kind regards,

Paul Stoffers

Christoph Paeper

unread,

May 7, 2004, 8:21:42 AM5/7/04

to

Jim Riley wrote:
> On Thu, 06 May 2004 08:55:47 +0200, Klaus von der Heyde
>

>> gallons, requiring an additional conversion factor (it is an
>> integer, at least: 231 inł, I had to look this up somewhere).
>
> Just remember that it factors into 3 x 7 x 11 (3 of the 5 smallest
> primes, leaving out the two used for the metric system 2 and 5).

Makes perfect sense in a system that mostly uses 2, 3 and sometimes 5 as
base factors, of course. The only two instances of 7 I could find were 5 × 7
= 35 gallons in a petroleum barrel and 2 × 3 × 7 = 42 gallons in a US
barrel; 11 occurs only in US survey units: 1 rod/pole/perch = 198 inches = 2
× 3 × 3 × 11 inches.

--
Dealing with trolls can be fun, if you are already standing on the desired
end of the bridge.

Christoph Paeper

unread,

May 7, 2004, 9:11:10 AM5/7/04

to

Jim Riley wrote:
> On Thu, 6 May 2004 18:54:01 +0200, Christoph Paeper

>> *Klaus von der Heyde* <uzs...@uni-bonn.de>:
>>> Jim Riley wrote:
>>>
>>>> Say you have a tank that is .3 by .3 by .4.
>>>
>>> Is that 0.3 m by 0.3 m by 0.4 m?
>>
>> Or if one prefers 3/10 m by 3/10 m by 4/10 m.
>

> I just re-measured it: is 35 cm by 32 cm by 44 cm.

That doesn't make it harder, just increases the number of significant
digits. How would you have done it with inches, by the way (with the same
precision)?

>>>> Then why should the US switch to SI?
>>
>> To save money and earn more.
>
> How much would I save if I didn't have to use factors of 60 and 24

(Doesn't a US-American day have 1 + 12 + 11 hours? Something like that.)

> for measuring time?

I take that to mean that you understand and agree in general.
Nobody is happy about the time issue for which there seems to be no good
solution, but the SI itself only uses seconds. Not that the Imperial System
was using better units.

>> Well, at least a register ton is 100 cubic feet. (It seems they like
>> to write it out just like on street signs.)
>
> What is a "register ton"?

100 ftł ;-P
Ask your local shipyard.

> What do you mean by "write it out just like on street sign"?

For instance "Speed limit 55 mph" instead of just big black "55" on white or
yellow background in a disc with red border, like most countries do (of
course an indication of speed unit used would help in this case).

Btw., someone suggested lately, the USA should use m/s on speed limit signs
when becoming serious about getting metric. I don't think that is such a
good idea, because the values are to close to each other:

18 km/h 5 m/s 11.18 mi./h
30 km/h 8.3Ż m/s 18.64 mi./h
36 km/h 10 m/s 22.37 mi./h
48.28 km/h 13.41 m/s 30 mi./h
50 km/h 13.8Ż m/s 31.07 mi./h
54 km/h 15 m/s 33.55 mi./h
70 km/h 19.4Ż m/s 43.50 mi./h
72 km/h 20 m/s 44.74 mi./h
88.51 km/h 24.59 m/s 55 mi./h
90 km/h 25 m/s 55.92 mi./h
100 km/h 27.7Ż m/s 62.14 mi./h
104.61 km/h 29.06 m/s 65 mi./h
108 km/h 30 m/s 67.11 mi./h
112.65 km/h 31.29 m/s 70 mi./h
120 km/h 33.3Ż m/s 74.56 mi./h
126 km/h 35 m/s 78.29 mi./h

OTOH for Americans it's roughly a factor 2 calculation and for us Metricians
it would mean an increase of allowed speed when rounded to the next number
divisible by 5 in most cases.

> Do you mean like writing "Road", "Street", "Aveneue"
> and "Boulevard" brather than "RD", "ST", "AVE", and "BLVD"?

No. (I think putting a dot after an abbreviation makes more sense than
uppercasing it, which makes it look like an acronym, though.)
The one thing I liked about US street signs was the indication of general
direction (north / east / south / west) on highways.

>> Quick, how many cubic inches are there in one cubic foot?
>

> How many cubic centimeters in a cube that is 12 centimeters on a side?

Wrong analogy, you should have asked me how many cubic centimeters there are
in a cubic decimeter, liter or cubic meter. I take your response to mean,
that you know the Imperial System factors are insane.

--
Nothing is lost until you begin to look for it.

Do not answer

unread,

May 7, 2004, 11:46:40 AM5/7/04

to

Jim Riley wrote:
> On Thu, 06 May 2004 08:55:47 +0200, Klaus von der Heyde
> <uzs...@uni-bonn.de> wrote:
>
>
>>Jim Riley wrote:
>>
>>
>>>If you are doing it in your head it may be. Say you have a tank that
>>>is .3 by .3 by .4.
>>
>>Is that 0.3 m by 0.3 m by 0.4 m?
>
>
> If you are doing this in your head, would you add the units? You
> either just measured your tank or estimated its dimensions.
>
>
>>>3 times 3 times 4 is 24.
>>
>>So, you want to calculate in decimetres, so:
>
>
> Why do I want to calculate in decimeters? I know that the volume of a
> rectangular solid is the product of width times depth times height.
> Who measures things in decimeters? People on this group are condemned
> for using centimeters.

Because it's easier to calculate 3x3x4 than 0.3x0.3x0.3. Then you
might get problems with the number of zeros around the decimal
point like in your example.

Br,

Brian Inglis

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May 7, 2004, 1:28:33 PM5/7/04

to

On Wed, 05 May 2004 21:37:30 GMT in misc.metric-system, Jim Riley
<jim...@pipeline.com> wrote:

>Few people live in Finland or Alaska. Their experience is atypical
>for most of the world.

Few people live in the USA.
Their units are unknown to most of the world.

--
Thanks. Take care, Brian Inglis Calgary, Alberta, Canada

Brian....@CSi.com (Brian dot Inglis at SystematicSw dot ab dot ca)
fake address use address above to reply

Joona I Palaste

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May 7, 2004, 1:58:12 PM5/7/04

to

Brian Inglis <Brian....@systematicsw.invalid> scribbled the following:

> On Wed, 05 May 2004 21:37:30 GMT in misc.metric-system, Jim Riley
> <jim...@pipeline.com> wrote:
>>Few people live in Finland or Alaska. Their experience is atypical
>>for most of the world.

> Few people live in the USA.
> Their units are unknown to most of the world.

Alaska *is* in the USA.

--
/-- Joona Palaste (pal...@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/

"You have moved your mouse, for these changes to take effect you must shut down
and restart your computer. Do you want to restart your computer now?"
- Karri Kalpio

Jim Riley

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May 7, 2004, 8:10:11 PM5/7/04

to

On Fri, 07 May 2004 17:28:33 GMT, Brian Inglis
<Brian....@SystematicSw.ab.ca> wrote:

>On Wed, 05 May 2004 21:37:30 GMT in misc.metric-system, Jim Riley
><jim...@pipeline.com> wrote:
>
>>Few people live in Finland or Alaska. Their experience is atypical
>>for most of the world.
>
>Few people live in the USA.

Your "point" is irrelevant to this discussion.

Most people on Earth live where the maximum daytime temperature in
summer is as hot or hotter than in the United States. This is
irrespective of which temperature scale is used.

It makes no sense to include a range for "hot day" that is based on
the experience of those who live in the near Arctic (and is identical
to the high temperature for a comfortable office) and ignores the
experience of the overwhelming majority of the people.

--
Jim Riley

Jim Riley

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May 7, 2004, 8:19:30 PM5/7/04

to

On Fri, 7 May 2004 02:50:44 +0200, Christoph Paeper
<christop...@nurfuerspam.de> wrote:

>*Jim Riley* <jim...@pipeline.com>:
>> On Thu, 6 May 2004 00:40:24 +0200, Christoph Paeper
>>
>>> I believe everyone using are and hectare knows, that they form a factor
>>> 100 series starting with square meter and ending with square kilometer.
>>
>> How did they come to know this?
>
>How did you come to know the factors between inch, foot and yard? Are and
>hectare just have much simpler factors, although not really in compliance
>with SI's standard 10訟dimension.

It may be harder to remember when all the factors are more or less the
same, than if they are unique. I think one reason that I have
difficulty remembering the factors between liquid measurement (cups,
pints, quarts, and gallons) is that they are all either 2 or 4.

--
Jim Riley

Jim Riley

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May 7, 2004, 11:35:26 PM5/7/04

to

On Fri, 7 May 2004 15:11:10 +0200, Christoph Paeper
<christop...@nurfuerspam.de> wrote:

>Jim Riley wrote:
>> On Thu, 6 May 2004 18:54:01 +0200, Christoph Paeper
>>> *Klaus von der Heyde* <uzs...@uni-bonn.de>:
>>>> Jim Riley wrote:
>>>>
>>>>> Say you have a tank that is .3 by .3 by .4.
>>>>
>>>> Is that 0.3 m by 0.3 m by 0.4 m?
>>>
>>> Or if one prefers 3/10 m by 3/10 m by 4/10 m.
>>
>> I just re-measured it: is 35 cm by 32 cm by 44 cm.
>
>That doesn't make it harder, just increases the number of significant
>digits. How would you have done it with inches, by the way (with the same
>precision)?

I doubt that I (or anyone else) would have converted 35 cm to 3.5 dm
or (3 1/2) /10 m.

14 in x 13 in x 17 in. I'd probably use a calculator, though I might
estimate it as roughly 15**3 or about 3300 cubic inches. I'd then
either look up the number of cubic inches per gallon or have it
memorized, and divide that into the volume in cubic inches.

Then I'd post to an aquarium group to find out whether aquarium
dimensions are measured exterior or interior to the glass, and whether
the volume is specified for a tank filled to the lip or not.

>>>>> Then why should the US switch to SI?
>>>
>>> To save money and earn more.
>>
>> How much would I save if I didn't have to use factors of 60 and 24
>
>(Doesn't a US-American day have 1 + 12 + 11 hours? Something like that.)

2 dozen.

>> What do you mean by "write it out just like on street sign"?
>
>For instance "Speed limit 55 mph" instead of just big black "55" on white or
>yellow background in a disc with red border, like most countries do (of
>course an indication of speed unit used would help in this case).

That would be a 'highway sign' or a 'road sign'. A 'street sign'
identifies the name of a street.

Standard practice is not to specify the units on speed limit signs,
unless it is specified in km/h, see:

http://mutcd.fhwa.dot.gov/ser-shs_millennium_met.htm

A curiousity is that load limit signs, if specified in tons (2000 lb),
is '10 T', and if in specified in metric tons (1000 kg), is specified
as '10 t'.

--
Jim Riley

Jim Riley

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May 8, 2004, 1:44:37 AM5/8/04

to

On Fri, 7 May 2004 13:06:20 +0200, "Paul Stoffers"
<PSt_...@hetnet.nl> wrote:

>"Jim Riley" <jim...@pipeline.com> schreef in bericht
>news:rIfmc.6503$a47....@newsread3.news.atl.earthlink.net

>> Then why should the US switch to SI?

>>
>There's one reason that hasn't been mentioned yet, to my surprise: trade, or
>more in general: communication. I wouldn't have any trouble making a dish
>using a recipe with ounces and pints, *if I had scales and a measuring cup
>indicating those units*, but I don't. I also do not see the difference in
>setting a Celsius temperature on an oven with a Celsius scale, or doing the
>same with a "Fahrenheit" oven, but *I* only have an oven with Celsius
>indication. I do not intend to have two sets of kitchen utensils.

But it would cause a communication problem in the United States to
convert. Most people have equipment that measures in English units.
Switching would cause confusion, and could be a health and safety
convern. If the speed limit is increased to "110", there might be an
increase in road accidents unless all the speedometers are replaced.
Someone using a metric recipe on a Fahrenheit stove, might undercook
meat.

--
Jim Riley

Matthew Smith

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May 8, 2004, 3:00:49 AM5/8/04

to

In article <9t_mc.9088$8S1....@newsread2.news.atl.earthlink.net>,
Jim Riley <jim...@pipeline.com> wrote:

> But it would cause a communication problem in the United States to
> convert. Most people have equipment that measures in English units.
> Switching would cause confusion, and could be a health and safety
> convern. If the speed limit is increased to "110", there might be an
> increase in road accidents unless all the speedometers are replaced.
> Someone using a metric recipe on a Fahrenheit stove, might undercook
> meat.

Are you suggesting the population of the United States is incapable of
doing what many other countries have done? I suppose after seeing an
episode of Newlyweds on TV I could agree with you.

Klaus von der Heyde

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May 8, 2004, 2:33:51 AM5/8/04

to

Jim Riley wrote:

> It may be harder to remember when all the factors are more or less the
> same, than if they are unique.

The factors for area and volume, 100 = 10² and 1000 = 10³ can be
derived from the factor 10 of the base lengths.

> I think one reason that I have
> difficulty remembering the factors between liquid measurement (cups,
> pints, quarts, and gallons) is that they are all either 2 or 4.

This happens because these units are set with no consistent system
behind. To the unaware it is not even clear that they are all used to
measure volumes.

If you really would like to make a point regarding not-so-easy to
remember factors: the relations of prefixes below µ and above G to
their corresponding factors are not obvious to everyone. There is the
alternative of using exponential notation (e.g. 7.5 * 10^-12 m) instead.

Klaus

Klaus von der Heyde

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May 8, 2004, 3:06:53 AM5/8/04

to

Jim Riley wrote:

> 14 in x 13 in x 17 in. I'd probably use a calculator,

Try 14 1/4 in, 12 5/8 in and 17 3/16 in instead, and compare the
efford needed to that for 362 mm, 321 mm, and 437 mm. It takes
exactly 2 multiplications in metric, as expected for volumes.
By the way, simple electronic calculators do not allow the input
of fractions like 5/8 in a convenient fashion.

> though I might
> estimate it as roughly 15**3 or about 3300 cubic inches.

I thought we would like to have exact results, not estimations.
(of your previous example)
Estimation in metric: 4 dm * 3 dm * 4 dm = 48 dm³.
Exact in metric: 3.5 dm * 3.2 dm * 4.4 dm = 49.28 dm³.

> I'd then
> either look up the number of cubic inches per gallon or have it
> memorized, and divide that into the volume in cubic inches.

It is exactly this division step that is much simpler with metric
units, because it consists of just shifting a comma, either before
the multiplication, as I did using dm, or afterwards, if you perfer
litres to cm³.

Klaus

Joona I Palaste

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May 8, 2004, 3:10:36 AM5/8/04

to

Matthew Smith <mat...@macxxx.com> scribbled the following:

I have asked people on this newsgroup why the US can't convert to
metric when pretty much the whole of the Europe successfully converted
to metric over a hundred years ago. The best answer I have got is that
back then, technology and international communication was not so
advanced, so there was less hassle involved in changing the entire
measurement system.
Then of course there are some for whom it's a matter of pride, who
abhor the very thought of the USA listening to someone else's opinion,
because it implies that the USA can't dictate the whole world's
politics as it pleases. Those people don't deserve being taken
seriously.

--
/-- Joona Palaste (pal...@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/

"I wish someone we knew would die so we could leave them flowers."
- A 6-year-old girl, upon seeing flowers in a cemetery

Paul Stoffers

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May 8, 2004, 7:22:42 AM5/8/04

to

"Jim Riley" <jim...@pipeline.com> schreef in bericht

news:9t_mc.9088$8S1....@newsread2.news.atl.earthlink.net

True. I wonder what would happen if that Someone used a Fahrenheit recipe on
a metric stove :). My point is that communication problems allready exist.
There are ofcourse no problems just as long as you stay on your "unit
island" and I stay on mine. My "unit island" is bigger anyway. Nevertheless
I would like to trade, communicate, exchange information with your island as
well.

I donot expect the US to change units overnight. This will take time and,
initially, cost money. Take your time, invest money. And in the end it will
save money.

Start with teaching children in school the metric units, as well as the
English units. Cookery books would have "dual" recipes. Stove manufacturers
could fit their stoves with a dual temperature setting for the time being.
They allready do (if they want to sell the same stove all over the world) or
allready make two types of stove. Car manufacturers now have to be very
carefull not to put an US speedometer in a EU-market car vice versa. They
have to keep two types of speedometers in stock. They could make the US type
a dual type. Car drivers would have to adapt, but with sufficiently
distinctive km/h-signs this shouldn't be a problem. The next generation will
know only km/h speed limits. Actually, in Ireland they are converting to
km/h speed limits just now.

In about ten years al the equipment in your house will probably be replaced.
Replace them with "dual type" equipment. In the next ten years or so you can
get accustomed with the metric units. When you have to replace equipment
again (in, say, 20 years from now) you'll buy "metric only".

The benefits to the industry and to consumers would be huge. No need for
both metric and US parts and models. Stock management will be a lot more
cost efficient. Production, therefore products, will be cheaper. Recipes
will no longer fail because of confusing temperature settings. We could
compare the maximum speed and fuel consumption of our cars in a moment. The
tyre pressure would be indicated in one unit only. (Preferably Pa or kPa,
but as we're not always consistent, "bar" or "atm" probably would be used.)

The EU is growing and becoming more and more important. In future European
Directives will (or allready have?) prohibit the use of non-metric units in
commercial and legal applications (trade, taxes, labeling, license
applications, user manuals, etc). Asia and Africa are developing
economically as well, using metric units. Consumers will buy whatever they
need all over the world, but they will buy metric goods only. Unless Uncle
Sam wants to become totally isolated economically, he'd better convert to
metric!

Kind Regards,

Paul - resistance is futile, you will be assimilated - Stoffers

Markus Kuhn

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May 8, 2004, 11:12:13 AM5/8/04

to

Jim Riley <jim...@pipeline.com> writes:
>But it would cause a communication problem in the United States to
>convert. Most people have equipment that measures in English units.

Experience from all the countries who switched in the
1970s showed that this equipment can usually be replaced or
modified at very little cost, and where this is not the case,
rather simple and practical workarounds can be found until
the equipment reaches the end of its lifetime. It is true that
metrication can lead to a very brief economic boom for the
local measurement equipment industry. Nothing wrong with that,
if they give you a shiny new caliper at work.

>Switching would cause confusion, and could be a health and safety
>convern.

Actual experience from people who have done this suggests otherwise.

>If the speed limit is increased to "110", there might be an
>increase in road accidents unless all the speedometers are replaced.

Actual experience from countries who have switched suggests that this
is not a problem at all in practice.

>Someone using a metric recipe on a Fahrenheit stove, might undercook
>meat.

These two scales are a factor 2 apart in the range relevant for
kitchen oven usage. As the useful ranges of kitchen oven temperatures
do not overlap, only an extremely inexperienced oven user could
be expected to make such a mistake. Extremely inexperienced kitchen
users probably face far more lethal dangers in that environment.

May be what distinguishes the US from most other countries
is the inability of a significant part of the population to
estimate and discuss risk in a reasonable and rational way. This
would manifest itself in recurring discussions of numerous irrelevant,
practically negligible, and often hillarious risks, e.g. kitchen
accidents due to metrication, aircraft losses due to passengers
carrying nail clippers, etc.

Markus

Brian Inglis

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May 8, 2004, 1:11:05 PM5/8/04

to

On Fri, 7 May 2004 14:21:42 +0200 in misc.metric-system, Christoph
Paeper <christop...@nurfuerspam.de> wrote:

>Jim Riley wrote:
>> On Thu, 06 May 2004 08:55:47 +0200, Klaus von der Heyde
>>
>>> gallons, requiring an additional conversion factor (it is an

>>> integer, at least: 231 in³, I had to look this up somewhere).

>>
>> Just remember that it factors into 3 x 7 x 11 (3 of the 5 smallest
>> primes, leaving out the two used for the metric system 2 and 5).
>
>Makes perfect sense in a system that mostly uses 2, 3 and sometimes 5 as
>base factors, of course. The only two instances of 7 I could find were 5 × 7
>= 35 gallons in a petroleum barrel and 2 × 3 × 7 = 42 gallons in a US
>barrel; 11 occurs only in US survey units: 1 rod/pole/perch = 198 inches = 2
>× 3 × 3 × 11 inches.

1 chain = 22 yards

Paul Hobson

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May 8, 2004, 5:18:59 PM5/8/04

to

"Christoph Paeper" <christop...@nurfuerspam.de> wrote in message
news:c7g1te$1jdd$1...@ariadne.rz.tu-clausthal.de...

> Btw., someone suggested lately, the USA should use m/s on speed limit
signs
> when becoming serious about getting metric. I don't think that is such a
> good idea, because the values are to close to each other:
>
> 18 km/h 5 m/s 11.18 mi./h

> 30 km/h 8.3¯ m/s 18.64 mi./h

> 36 km/h 10 m/s 22.37 mi./h
> 48.28 km/h 13.41 m/s 30 mi./h

> 50 km/h 13.8¯ m/s 31.07 mi./h

> 54 km/h 15 m/s 33.55 mi./h

> 70 km/h 19.4¯ m/s 43.50 mi./h

> 72 km/h 20 m/s 44.74 mi./h
> 88.51 km/h 24.59 m/s 55 mi./h
> 90 km/h 25 m/s 55.92 mi./h

> 100 km/h 27.7¯ m/s 62.14 mi./h

> 104.61 km/h 29.06 m/s 65 mi./h
> 108 km/h 30 m/s 67.11 mi./h
> 112.65 km/h 31.29 m/s 70 mi./h

> 120 km/h 33.3¯ m/s 74.56 mi./h

> 126 km/h 35 m/s 78.29 mi./h
>
> OTOH for Americans it's roughly a factor 2 calculation and for us
Metricians
> it would mean an increase of allowed speed when rounded to the next number
> divisible by 5 in most cases.

I still think m/s on road signs is a bad idea. It's simply not practical.
While driving over long distances, it's easier to think of time in hours and
then figure out how long it'll take given the length in km (or miles) and
your speed in km (or miles) per hour.

paul

______________________________
Paul Hobson
General Manager, Under the Couch
Georgia Institute of Technology
http://www.underthecouch.org

Jukka K. Korpela

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May 8, 2004, 5:54:51 PM5/8/04

to

"Paul Hobson" <gtg...@mail.gatech.edu> wrote:

> I still think m/s on road signs is a bad idea. It's simply not
> practical.

What is practical depends greatly on habits and views.

Once people thought it was practical to express the power of a car in
horsepowers. This went on long after any comparison with the power of
horse had lost all practical significance. (Besides, the horsepower was
actually more than an average horse's power. But I digress.) People might
still have said that the horsepower is practical and the watt (even when
using the kilowatt) is simply not practical. But the only reason was that
people were used to the old unit. It had to change sooner or later; the
sooner the better. (Actually, I think there might even be countries where
this change is still in progress.)

> While driving over long distances, it's easier to think of
> time in hours and then figure out how long it'll take given the
> length in km (or miles) and your speed in km (or miles) per hour.

Well, then start thinking of time in seconds and kiloseconds. :-)

Seriously, if you think about 70 km/h for example, it may sound pretty
slow, especially if you have long way to go and little time. Therefore,
it is useful to think of it as about 19 m/s. That is, your car moves
19 meters in a second. This should make you think about safety issues.
How much can you, or your car, do in a second when something unexpected
happens?

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Stefano MacGregor

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May 8, 2004, 7:41:04 PM5/8/04

to

"Paul Stoffers" <PSt_...@hetnet.nl> wrote in message news:<c7ige9$q22$1...@reader08.wxs.nl>...

> Car manufacturers now have to be very careful not to put a US
> speedometer in a EU-market car, and vice versa. They have to keep

> two types of speedometers in stock. They could make the US type
> a dual type.

They already do. US Speedometers are calibrated in MPH on the outside
of the dial, and in km/h just inside that. The next step would be to
reverse the two scales, and post speed limits in both units, so just
under the rectangular sign that says "SPEED / LIMIT / 55 / MPH" would
be a circular one that says "88". Later, make the metric speed the
round number, "90", and put it above the MPH sign. Finally, leave off
the Flintstone-unit sign.

Distances to the next exit should come along with all this. The sign
that now says "THUNDERBIRD ROAD 3/4 MILE" could just as well read
"THUNDERBIRD ROAD 1200 m (3/4 MILE)" for a while, and in a few years
leave off the miles.

We =can= catch up with the rest of the world here, but it will take us
a while. Eventually, we may even realize that many people do not
speak English.

--
Stefano
http://www.steve-and-pattie.com/esperantujo

Don Aitken

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May 8, 2004, 11:34:27 PM5/8/04

to

On 8 May 2004 16:41:04 -0700, esper...@yahoo.com (Stefano
MacGregor) wrote:

The experience of other countries suggests that this is probably not
the way to go about it. If you provide information in two sets of
units, the unfamiliar one is simply ignored. The best approach is the
"big bang"; after M-day the old units disappear as quickly as can be
managed, and people adapt to the new ones because they actually need
to.

--
Don Aitken

Mail to the addresses given in the headers is no longer being
read. To mail me, substitute "clara.co.uk" for "freeuk.com".

Markus Kuhn

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May 9, 2004, 6:16:57 AM5/9/04

to

esper...@yahoo.com (Stefano MacGregor) writes:
>They already do. US Speedometers are calibrated in MPH on the outside
>of the dial, and in km/h just inside that. The next step would be to
>reverse the two scales, and post speed limits in both units, so just
>under the rectangular sign that says "SPEED / LIMIT / 55 / MPH" would
>be a circular one that says "88". Later, make the metric speed the
>round number, "90", and put it above the MPH sign. Finally, leave off
>the Flintstone-unit sign.
>
>Distances to the next exit should come along with all this. The sign
>that now says "THUNDERBIRD ROAD 3/4 MILE" could just as well read
>"THUNDERBIRD ROAD 1200 m (3/4 MILE)" for a while, and in a few years
>leave off the miles.

Dual labeling road signs seems like a very bad idea. You double the
conversion cost, because the signs have to be modified twice, not just once.
You also slow down the conversion, because practice shows that with
dual labeling, people just stick to their old units, as they are not
forced to seriously consider the new unit. And you confuse people by
doubling the amount of information presented. The only way to do this
properly is to switch completely within a few days, as Canada did for
example for all speed signs over the Labor Day weekend of 1977.
Distance signs you can replace gradually over a few weeks or months,
as they are not so safety critical, and as they usually show a unit
anyway.

The history of Canadian metrication:

http://lamar.colostate.edu/~hillger/internat.htm#canada

Markus

Christoph Paeper

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May 9, 2004, 3:49:14 PM5/9/04

to

Jim Riley wrote:
> On Fri, 7 May 2004 15:11:10 +0200, Christoph Paeper

>> Jim Riley wrote:
>>> On Thu, 6 May 2004 18:54:01 +0200, Christoph Paeper
>

>>>> Or if one prefers 3/10 m by 3/10 m by 4/10 m.
>>>
>>> I just re-measured it: is 35 cm by 32 cm by 44 cm.
>>
>> That doesn't make it harder, just increases the number of significant
>> digits.
>

> I doubt that I (or anyone else) would have converted 35 cm to 3.5 dm
> or (3 1/2) /10 m.

Yes, but maybe to 35/100 m or 35/10² m instead of 3/10 m.

> 14 in x 13 in x 17 in.

|| How would you have done it with inches, by the way
|| (with the same precision)?
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

> A curiousity is that load limit signs, if specified in tons (2000 lb),
> is '10 T',

So the 'long ton' is never used?

> and if in specified in metric tons (1000 kg), is specified as '10 t'.

I've heard that it is been/being replaced in some companies by megagram (Mg)
to be better understood by US-American engineers.

--
Only wimps use tape backup: _real_ men just upload their important stuff on FTP,
and let the rest of the world mirror it. (Linus Torvalds)

Jim Riley

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May 9, 2004, 7:37:55 PM5/9/04

to

On Sat, 08 May 2004 09:06:53 +0200, Klaus von der Heyde
<uzs...@uni-bonn.de> wrote:

>Jim Riley wrote:
>
>> 14 in x 13 in x 17 in. I'd probably use a calculator,
>
>Try 14 1/4 in, 12 5/8 in and 17 3/16 in instead, and compare the
>efford needed to that for 362 mm, 321 mm, and 437 mm. It takes
>exactly 2 multiplications in metric, as expected for volumes.
>By the way, simple electronic calculators do not allow the input
>of fractions like 5/8 in a convenient fashion.

14.25 x 12.625 x 17.1875 / 231 = 13.39 gallons

362 x 321 x 437 = 50780274 ľl

I think you are missing a division in the metric answer. It would be
quite ordinary to know the decimal fraction equivalents of all
multiples of 1/16 between 0 and 1. And while the simplest electronic
calculators may not have a way to input mixed fractions, cheap
electronic calculators do.

And we are overlooking numerous practical problems in converting from
dimensions to volume which are far more important than knowing how
many cubic inches there are per gallon. Are the dimensions measured
exterior to the tank, or the interior? The external dimensions are
important in making sure that we have enough space to place the tanks,
the internal in determining how much water the tank will hold. We are
ignoring whether the tank is truly a rectangular solid, whether a
frame intrudes, or how much it will deform when filled with water.
We are ignoring whatever conventions are used in specifying tank
capacity, for example whether it is filled to the lip or not.

>> though I might
>> estimate it as roughly 15**3 or about 3300 cubic inches.
>
>I thought we would like to have exact results, not estimations.
>(of your previous example)

>Estimation in metric: 4 dm * 3 dm * 4 dm = 48 dmł.
>Exact in metric: 3.5 dm * 3.2 dm * 4.4 dm = 49.28 dmł.

>
>> I'd then
>> either look up the number of cubic inches per gallon or have it
>> memorized, and divide that into the volume in cubic inches.
>
>It is exactly this division step that is much simpler with metric
>units, because it consists of just shifting a comma, either before
>the multiplication, as I did using dm, or afterwards, if you perfer

>litres to cmł.

How many calculators permit you to shift the decimal point?

--
Jim Riley

Jim Riley

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May 9, 2004, 9:54:30 PM5/9/04

to

On Sat, 8 May 2004 13:22:42 +0200, "Paul Stoffers"
<PSt_...@hetnet.nl> wrote:

They'd be billed in BTU.

> My point is that communication problems allready exist.
>There are ofcourse no problems just as long as you stay on your "unit
>island" and I stay on mine. My "unit island" is bigger anyway. Nevertheless
>I would like to trade, communicate, exchange information with your island as
>well.

My unit island is large enough and isolated enough to sustain its own
units. If necessary for trade, adaptors can be used.

>I donot expect the US to change units overnight. This will take time and,
>initially, cost money. Take your time, invest money. And in the end it will
>save money.

If it would save money, wouldn't it be worth also getting rid of the
hour and the minute? Define a new unit of time equal to 1/100,000 of
a day, as well as associated units such as the hertz, ampere, and ohm.

>Start with teaching children in school the metric units, as well as the
>English units. Cookery books would have "dual" recipes. Stove manufacturers
>could fit their stoves with a dual temperature setting for the time being.
>They allready do (if they want to sell the same stove all over the world) or
>allready make two types of stove. Car manufacturers now have to be very
>carefull not to put an US speedometer in a EU-market car vice versa.

American children are already multimetric from elementary school.
Stoves with digital controls are probably already dual system. If
they have a timer, this could support the new time unit. The same
goes for speedometers. Models sold into the EU-market could simply
have the switch button disabled.

> They
>have to keep two types of speedometers in stock. They could make the US type
>a dual type. Car drivers would have to adapt, but with sufficiently
>distinctive km/h-signs this shouldn't be a problem. The next generation will
>know only km/h speed limits. Actually, in Ireland they are converting to
>km/h speed limits just now.

With more and more cars equipped with navigation systems, do we need
speed limit "signs"? This way those who cling to hours would not have
to switch.

>In about ten years al the equipment in your house will probably be replaced.
>Replace them with "dual type" equipment. In the next ten years or so you can
>get accustomed with the metric units. When you have to replace equipment
>again (in, say, 20 years from now) you'll buy "metric only".

The house itself will still be built in English units. The main roads
will still be a mile apart.

>The benefits to the industry and to consumers would be huge. No need for
>both metric and US parts and models. Stock management will be a lot more
>cost efficient. Production, therefore products, will be cheaper. Recipes
>will no longer fail because of confusing temperature settings. We could
>compare the maximum speed and fuel consumption of our cars in a moment. The
>tyre pressure would be indicated in one unit only. (Preferably Pa or kPa,
>but as we're not always consistent, "bar" or "atm" probably would be used.)

Is this really an advantage to anyone but the manufacturers of tire
gauges?

>The EU is growing and becoming more and more important. In future European
>Directives will (or allready have?) prohibit the use of non-metric units in
>commercial and legal applications (trade, taxes, labeling, license
>applications, user manuals, etc). Asia and Africa are developing
>economically as well, using metric units. Consumers will buy whatever they
>need all over the world, but they will buy metric goods only. Unless Uncle
>Sam wants to become totally isolated economically, he'd better convert to
>metric!

Asia will have no problems producing consumer products that are based
on American standards. Japan had no trouble producing right-hand
drive vehicles. User manuals, labels, etc. will have to be translated
into foreign languages anyhow.

--
Jim Riley

Jim Riley

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May 9, 2004, 10:28:02 PM5/9/04

to

On 8 May 2004 15:12:13 GMT, n04W19...@cl.cam.ac.uk (Markus Kuhn)
wrote:

>Jim Riley <jim...@pipeline.com> writes:

>>But it would cause a communication problem in the United States to
>>convert. Most people have equipment that measures in English units.
>
>Experience from all the countries who switched in the
>1970s showed that this equipment can usually be replaced or
>modified at very little cost, and where this is not the case,
>rather simple and practical workarounds can be found until
>the equipment reaches the end of its lifetime.

Wouldn't the same be true if the second were replaced as the unit of
time? There are real practical advantages to having 100,000 time
units in a day, as well as being able to have a single way to specify
velocity. Compared this to the meter, where the decision to base the
length of the meter on the distance from the equator to pole was
purely arbitrary and of no real practical value.

>It is true that
>metrication can lead to a very brief economic boom for the
>local measurement equipment industry. Nothing wrong with that,
>if they give you a shiny new caliper at work.

The clock manufacturers would benefit.

>>Switching would cause confusion, and could be a health and safety
>>convern.
>
>Actual experience from people who have done this suggests otherwise.

So there would be no problems in switching the time units?

>>Someone using a metric recipe on a Fahrenheit stove, might undercook
>>meat.
>
>These two scales are a factor 2 apart in the range relevant for
>kitchen oven usage. As the useful ranges of kitchen oven temperatures
>do not overlap, only an extremely inexperienced oven user could
>be expected to make such a mistake. Extremely inexperienced kitchen
>users probably face far more lethal dangers in that environment.

It could well be a matter of carelessness. Have you never walked into
the wrong room in a building because you were following an old path in
your brain? Why wouldn't someone set the oven for 200 degrees on a
Fahrenheit-gauged stove? After all, there are those who consider 25
degrees to be a hot day.

--
Jim Riley

Markus Kuhn

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May 10, 2004, 8:02:23 AM5/10/04

to

Jim Riley <jim...@pipeline.com> writes:
>How many calculators permit you to shift the decimal point?

I think it is an extremely common feature of any low-cost pocket
calculator targeted at the secondary education, scientific and
technical user:

For example, Casio's very nice school calculators had for over than 20
years now two buttons labelled ENG> and ENG< which allow you to change the
displayed exponential notation to the next higher/lower power of 10^3.

So you can switch the display of a number between

100000
100 x 10^3
0.1 x 10^6
0.0001 x 10^9

etc., which is very handy if want to know the number with
a certain SI prefix and you have already so many other details
in your head that you can't be bothered to shift the decimal
point mentally. I use that function all the time.

I suspect the button is are called ENG, because Casio believes that
mostly engineers what to tweak the scientific exponential notation
by factors of 10^3.

Even their entry-level model has it:

http://www.casio.co.uk/calculators/pdfs/FX83MS.pdf

Markus

Dr John Stockton

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May 10, 2004, 7:32:41 AM5/10/04

to

JRS: In article <c7m1vo$gbv$1...@ariadne.rz.tu-clausthal.de>, seen in
news:misc.metric-system, Christoph Paeper <christoph.paeper@nurfuerspam.
de> posted at Sun, 9 May 2004 21:49:14 :

>
>I've heard that it is been/being replaced in some companies by megagram (Mg)
>to be better understood by US-American engineers.

Potentially confusing, since the same characters are then used for
amount-of-substance as are used for the chemical symbol of a substance
not unknown in engineering.

It's the only case I can immediately think of where the chemical symbol
for a stable element matches a reasonable SI-type prefix+unit
combination.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk / ??.Stoc...@physics.org ©
Web <URL:http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, & links.
Correct <= 4-line sig. separator as above, a line precisely "-- " (SoRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "> " (SoRFC1036)

Christoph Paeper

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May 10, 2004, 3:25:43 PM5/10/04

to

*Dr John Stockton* <sp...@merlyn.demon.co.uk>:
>
> [Mg]

> It's the only case I can immediately think of where the chemical symbol
> for a stable element matches a reasonable SI-type prefix+unit
> combination.

Ignoring "stable" and making "prefix" optional, I found (without claiming
completeness):

F: Farad / Fluor
H: Henry / Hydrogen
K: Kelvin / Potassium (Kalium)
N: Newton / Nitrogen
S: Siemens / Sulfur
V: Volt / Vanadium
W: Watt / Wolfram

Pa: Pascal / Protactinium

Mg: Megagram / Magnesium
Mt: Megaton / Meitnerium
Tl: Teraliter / Thallium
Pm: Petameter / Promethium
Tm: Terameter / Thulium
Es: Exasecond / Einsteinium

Of these of course 'Mg' has the biggest chances of causing trouble.

--
To the optimist, the glass is half full.
To the pessimist, the glass is half empty.
To the engineer, the glass has an appropriate reserve space.
To the economist, the glass is twice as big as it needs to be.

Erik Max Francis

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May 10, 2004, 3:33:27 PM5/10/04

to

Christoph Paeper wrote:

> Of these of course 'Mg' has the biggest chances of causing trouble.

Seems to me like kelvin/potassium or newton/nitrogen is much more likely
to cause a conflict -- and they would have already if there were one.
Sounds like a mountain out of a mole hill to me. I would think that the
only case where using Mg (or N or K) would cause major ambiguities is
when there's nearly incomprehensible writing around it -- and that would
be ambiguous anyway, even without the unit/chemical symbol name.

--
__ Erik Max Francis && m...@alcyone.com && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
\__/ The only way to get rid of a temptation is to yield to it.
-- Oscar Wilde

Klaus von der Heyde

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May 10, 2004, 5:06:13 PM5/10/04

to

Christoph Paeper wrote:

> F: Farad / Fluor
> H: Henry / Hydrogen
> K: Kelvin / Potassium (Kalium)
> N: Newton / Nitrogen
> S: Siemens / Sulfur
> V: Volt / Vanadium
> W: Watt / Wolfram

C: Coulomb / Carbon
J: Joule / Iodine

> Mg: Megagram / Magnesium
[...]

My favourite:
1 As (ampere second) == 1 C (coulomb)
As (arseinc) != C (carbon)

Klaus

Jukka K. Korpela

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May 10, 2004, 5:43:48 PM5/10/04

to

Dr John Stockton <sp...@merlyn.demon.co.uk> wrote:

>>I've heard that it is been/being replaced in some companies by
>>megagram (Mg) to be better understood by US-American engineers.
>
> Potentially confusing, since the same characters are then used for
> amount-of-substance as are used for the chemical symbol of a
> substance not unknown in engineering.

The character string "Mg", as any simple combination of letters, can mean
a multitude of things in different notation systems and languages.
The SI notations are not meant to be globally unique in the sense that
they could not have any other interpretation _in other contexts and
systems_. Such uniqueness is impossible and unnecessary.

--
Yucca, http://www.cs.tut.fi/~jkorpela/

Jim Riley

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May 11, 2004, 6:37:47 AM5/11/04

to

On 10 May 2004 12:02:23 GMT, n04W20...@cl.cam.ac.uk (Markus Kuhn)
wrote:

>Jim Riley <jim...@pipeline.com> writes:

>>How many calculators permit you to shift the decimal point?
>
>I think it is an extremely common feature of any low-cost pocket
>calculator targeted at the secondary education, scientific and
>technical user:

I don't see such a shift function on my TI calculator. You would have
to multiply or divide by 1000 or 1 <EXP> 3. It does have a display
mode called <ENG> where the exponent is forced to a multiple of 3.

--
Jim Riley

Joona I Palaste

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May 11, 2004, 6:52:00 AM5/11/04

to

Jim Riley <jim...@pipeline.com> scribbled the following:

Well, my Casio CFX-9970G even has functions to type "engineering
symbols" such as G, M, k, m, µ or n. These act as constants with values
of 10^9, 10^6, 10^3, 10^(-3), 10^(-6) and 10^(-9) respectively. So
typing an engineering symbol after a number multiplies the number with
that value.
If your TI calculator doesn't have them, well then, blame TI. No one
ever said such functions would have to be on all calculators.
But I don't think this either proves or disproves the ease of the metric
system over the obsolete^Wimperial system.

--
/-- Joona Palaste (pal...@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/

"'It can be easily shown that' means 'I saw a proof of this once (which I didn't
understand) which I can no longer remember'."
- A maths teacher

Jim Riley

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May 11, 2004, 7:04:50 AM5/11/04

to

On Sun, 9 May 2004 21:49:14 +0200, Christoph Paeper
<christop...@nurfuerspam.de> wrote:

>Jim Riley wrote:

>> A curiousity is that load limit signs, if specified in tons (2000 lb),
>> is '10 T',
>
>So the 'long ton' is never used?

Not for load limits (on bridges, etc)

>> and if in specified in metric tons (1000 kg), is specified as '10 t'.

>I've heard that it is been/being replaced in some companies by megagram (Mg)
>to be better understood by US-American engineers.

Since a short ton is 2.3% lighter than a metric ton, a
misinterpretation of 't' to mean a short ton simply provides a
slightly larger safety margin.

--
Jim Riley

Philip Kendall

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May 11, 2004, 7:08:42 AM5/11/04

to

In article <mr2oc.5724$KE6....@newsread3.news.atl.earthlink.net>,

Jim Riley <jim...@pipeline.com> wrote:
>
>Since a short ton is 2.3% lighter than a metric ton, a
>misinterpretation of 't' to mean a short ton simply provides a
>slightly larger safety margin.

"This structure requires at least 100 t of counterweight at point X to
ensure stability".

Cheers,

Phil

--
Philip Kendall <pa...@srcf.ucam.org>
http://www.srcf.ucam.org/~pak21/

Message has been deleted

Christoph Paeper

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May 11, 2004, 12:29:32 PM5/11/04

to

*Jim Riley* <jim...@pipeline.com>:

> On Sun, 9 May 2004 21:49:14 +0200, Christoph Paeper
>

>> I've heard that [ton] is been/being replaced in some companies by

>> megagram (Mg) to be better understood by US-American engineers.
>
> Since a short ton is 2.3% lighter than a metric ton,

907 of 1000 kg is 97.7%? A long one is around 1016 kg.

The Avoirdupois units would work fine transitionally with the SI, if they
were (current definitions in brackets):

1 pound (#) = 500 g
(7000 grains = 454 g)
1 stone = ˝ quarter = 12˝ # = 6.25 kg
(14 # = 6.35 kg)
1 quarter = ź cwt. = 25 # = 12.5 kg
(ź long cwt. = 28 # = 12.7 kg)
1 hundredweight (cwt.) = 100 # = 50 kg
(short: 100 # = 45.4 kg;
long: 112 # = 50.8 kg)
1 ton = 20 cwt. = 2000 # = 1000 kg
(short: 20 short cwt. = 2000 # = 907 kg;
long: 20 long cwt. = 2240 # = 1016 kg)

That is a mixture of long and short definitions to come to even (kilo)gram
values. The largest offset would be the pound (and short cwt. and ton) with
ca. +10%. The factor 7 (in 'long' units) would be gone.
I ignored grains, drams and ounces, though.

A 25 mm inch based length system would have been nice, too. Volumes are a
bit more off, although one pint of 500 ml would probably be a good start,
making

1 quart = 1 l = 2 pints = ź gallon and
1 gallon = 4 l = 256 cubic inches.

Btw., what is or was the quarter that is eight bushels (= 32 pecks = 64
gallons) a quarter of?

> a misinterpretation of 't' to mean a short ton simply provides a
> slightly larger safety margin.

US company 1: "We'll sell you $product for 1000 $ per ton." (short)
US company 2: "We'll sell you $product for 1000 $ per ton." (metric)
US company 3: "We'll sell you $product for 1000 $ per ton." (long)

--
The Hitchhiker's Guide to the Galaxy:
"He was a dreamer, a thinker, a speculative philosopher,
or, as his wife would have it, an idiot."

Christoph Paeper

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May 11, 2004, 12:29:57 PM5/11/04

to

*Brian Inglis* <Brian....@SystematicSw.Invalid>:

> Christoph Paeper <christop...@nurfuerspam.de> wrote:
>
>> Makes perfect sense in a system that mostly uses 2, 3 and sometimes

>> 5 as base factors, of course. (...) 11 occurs only in US survey units:

>> 1 rod/pole/perch = 198 inches = 2 × 3 × 3 × 11 inches.
>
> 1 chain = 22 yards

Yes (or 4 rods), and

1 furlong = 10 chains
1 mile = 8 furlongs,

so 11 is indeed a factor in most length units above one meter (and the
link). Accordingly it's in larger areas, too, as

1 acre = 160 square rods = 1/640 square mile.

Funny craziness.
How it got into the comparably small inch-based definition of an US gallon
is mysterious, though. At least for me.

--
Ociffer, I swear to drunk, I'm not God!

Dr John Stockton

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May 11, 2004, 12:35:18 PM5/11/04

to

JRS: In article <Xns94E66ED9D1AE...@193.229.0.31>, seen in
news:misc.metric-system, Jukka K. Korpela <jkor...@cs.tut.fi> posted at
Mon, 10 May 2004 21:43:48 :

Impossible, inessential, but would be useful. What is essential is that
one should be aware of where confusion might ensue, and ensure that it
does not.

The Imperials have many ton[ne]s already; they should be able to cope
with the one that the rest of the world is familiar with.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
some Astro stuff via astro.htm, gravity0.htm; quotes.htm; pascal.htm; &c, &c.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

Esa A E Peuha

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May 12, 2004, 4:04:57 AM5/12/04

to

Christoph Paeper <christop...@nurfuerspam.de> writes:

> 1 acre = 160 square rods = 1/640 square mile.
>
> Funny craziness.

If you write "acre = chain * furlong", it actually makes some sense that
farmland was measured in pieces of exactly that shape.

--
Esa Peuha
student of mathematics at the University of Helsinki
http://www.helsinki.fi/~peuha/

Jim Riley

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May 12, 2004, 8:28:21 PM5/12/04

to

On 11 May 2004 10:52:00 GMT, Joona I Palaste <pal...@cc.helsinki.fi>
wrote:

>Jim Riley <jim...@pipeline.com> scribbled the following:

>> On 10 May 2004 12:02:23 GMT, n04W20...@cl.cam.ac.uk (Markus Kuhn)
>> wrote:
>>>Jim Riley <jim...@pipeline.com> writes:
>>>>How many calculators permit you to shift the decimal point?
>>>
>>>I think it is an extremely common feature of any low-cost pocket
>>>calculator targeted at the secondary education, scientific and
>>>technical user:
>
>> I don't see such a shift function on my TI calculator. You would have
>> to multiply or divide by 1000 or 1 <EXP> 3. It does have a display
>> mode called <ENG> where the exponent is forced to a multiple of 3.
>
>Well, my Casio CFX-9970G even has functions to type "engineering
>symbols" such as G, M, k, m, µ or n. These act as constants with values
>of 10^9, 10^6, 10^3, 10^(-3), 10^(-6) and 10^(-9) respectively. So
>typing an engineering symbol after a number multiplies the number with
>that value.

This sounds like it is more oriented towards data input, rather than
conversion. If I were to enter: "34 <c> x 27 <c> x 48 <c>", I would
have a volume in units of cubic meters. I don't think it is
particularly intuitive to then multiply by "1 <m>" or divide by "1
<k>" to convert to liters.

>If your TI calculator doesn't have them, well then, blame TI. No one
>ever said such functions would have to be on all calculators.

There is no reason to assess blame. Markus Kuhn asserted that it was
an extremely common feature to have a decimal shift capablity, which
implies that it is extremely rare to not have the capability.

My TI calculator does have one useful conversion key which permits
conversion from hours:minutes:seconds to hours (with a decimal
fraction). It also permits easy entry of mixed fractions so that

>Try 14 1/4 in, 12 5/8 in and 17 3/16 in instead, and compare the
>efford needed to that for 362 mm, 321 mm, and 437 mm. It takes
>exactly 2 multiplications in metric, as expected for volumes.
>By the way, simple electronic calculators do not allow the input
>of fractions like 5/8 in a convenient fashion.

14 <*> 1 <*> 4 X 12 <*> 5 <*> 8 X 17 <*> 3 <*> 16 / 231

quickly calculates a volume of 13.386 gallons. The <*> key which is
labeled [a b/c] functions somewhat like the [.] key. So at least on a
TI-34 calculator, working with mixed fractions is as easy as abc.

>But I don't think this either proves or disproves the ease of the metric
>system over the obsolete^Wimperial system.

Since we are referring to the system of units primarily used in the
United States, should we use the terminology used in the United States
(i.e. English rather than Imperial)?

--
Jim Riley

Jim Riley

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May 12, 2004, 8:38:50 PM5/12/04

to

On 11 May 2004 12:08:42 +0100, pa...@cam.ac.uk (Philip Kendall) wrote:

>In article <mr2oc.5724$KE6....@newsread3.news.atl.earthlink.net>,
>Jim Riley <jim...@pipeline.com> wrote:
>>
>>Since a short ton is 2.3% lighter than a metric ton, a
>>misinterpretation of 't' to mean a short ton simply provides a
>>slightly larger safety margin.
>
>"This structure requires at least 100 t of counterweight at point X to
>ensure stability".

I have never seen such a sign on a bridge. I don't think that on draw
bridges that the vehicles wishing to cross are used as counterweights.

--
Jim Riley

Jim Riley

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May 12, 2004, 10:31:19 PM5/12/04

to

On Tue, 11 May 2004 18:29:32 +0200, Christoph Paeper
<christop...@nurfuerspam.de> wrote:

>*Jim Riley* <jim...@pipeline.com>:
>> On Sun, 9 May 2004 21:49:14 +0200, Christoph Paeper
>>
>>> I've heard that [ton] is been/being replaced in some companies by
>>> megagram (Mg) to be better understood by US-American engineers.
>>
>> Since a short ton is 2.3% lighter than a metric ton,
>
>907 of 1000 kg is 97.7%? A long one is around 1016 kg.

I don't know where the '2.3%' came from. Maybe, I meant to type
'9.3%.

The context was in terms of road signs in the United States. As I
pointed out, standard practice is to not indicate MPH on speed limit
signs, but to include "km/h" and the warning "METRIC" (in yellow)
whenever metric speeds were indicated.

On the other hand, when load limits are specified, the units of either
short tons or metric tons is indicated through use of "T" or "t". I
found this somewhat strange in that there is a specific risk in
exceeding the load limit. I'm not sure where load limits are
specified in metric tons, unless it is along the Canadian border.

Dunno. If it were filled with water, it would be roughly a 1/4 ton.
Maybe with wheat or apples, it is closer.

The only reason that I know that a peck is unit of measurement is from
the song in which it is used as a measurement of love (a bushel and a
peck). A bushel is the size of a bushel basket.

>> a misinterpretation of 't' to mean a short ton simply provides a
>> slightly larger safety margin.
>
>US company 1: "We'll sell you $product for 1000 $ per ton." (short)
>US company 2: "We'll sell you $product for 1000 $ per ton." (metric)
>US company 3: "We'll sell you $product for 1000 $ per ton." (long)

You have to listen very closely to the salesman, he will either say
"Ton", "ton", or "tonne".

--
Jim Riley

Brian Inglis

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May 13, 2004, 3:58:34 AM5/13/04

to

On Thu, 13 May 2004 00:28:21 GMT in misc.metric-system, Jim Riley
<jim...@pipeline.com> wrote:

>Since we are referring to the system of units primarily used in the
>United States, should we use the terminology used in the United States
>(i.e. English rather than Imperial)?

Outside the US, English implies Imperial as opposed to US units, or
for someone familiar with usage in and out of the US, would be
ambiguous, so stating US units would be more informative.

--
Thanks. Take care, Brian Inglis Calgary, Alberta, Canada

Brian....@CSi.com (Brian dot Inglis at SystematicSw dot ab dot ca)
fake address use address above to reply

Brian Inglis

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May 13, 2004, 4:01:33 AM5/13/04

to

On Sun, 9 May 2004 21:49:14 +0200 in misc.metric-system, Christoph
Paeper <christop...@nurfuerspam.de> wrote:

>Jim Riley wrote:
>> On Fri, 7 May 2004 15:11:10 +0200, Christoph Paeper
>>> Jim Riley wrote:
>>>> On Thu, 6 May 2004 18:54:01 +0200, Christoph Paeper

>> A curiousity is that load limit signs, if specified in tons (2000 lb),

>> is '10 T',
>
>So the 'long ton' is never used?
>
>> and if in specified in metric tons (1000 kg), is specified as '10 t'.
>
>I've heard that it is been/being replaced in some companies by megagram (Mg)
>to be better understood by US-American engineers.

Whereas in the UK the US short (2000 lb) ton is relatively unknown.

Brian Inglis

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May 13, 2004, 4:36:22 AM5/13/04

to

On Tue, 11 May 2004 18:29:32 +0200 in misc.metric-system, Christoph
Paeper <christop...@nurfuerspam.de> wrote:

>*Jim Riley* <jim...@pipeline.com>:
>> On Sun, 9 May 2004 21:49:14 +0200, Christoph Paeper

>Btw., what is or was the quarter that is eight bushels (= 32 pecks = 64
>gallons) a quarter of?

a tun ~ 256 gallons (normally 252)

>US company 1: "We'll sell you $product for 1000 $ per ton." (short)
>US company 2: "We'll sell you $product for 1000 $ per ton." (metric)
>US company 3: "We'll sell you $product for 1000 $ per ton." (long)

As opposed to an assay ton (US/UK), a refrigeration ton, a ton of TNT,
or one of the following nautical tons:
register ton 100 ft^3 ship internal capacity
shipping ton US 40 ft^3 ship cargo freight
shipping ton UK 42 ft^3
displacement ton 35 ft^3 UK ton sea water volume
water ton 224 gallon UK fresh water per ton UK

Christoph Paeper

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May 13, 2004, 2:51:35 PM5/13/04

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*Brian Inglis* <Brian....@SystematicSw.Invalid>:

>
> Whereas in the UK the US short (2000 lb) ton is relatively unknown.

As far as I understand it, the Avoirdupois system, when introduced in
Britain and its colonies, was

1 ton = 20 hundredweights = 20×4 quarters = 20×4×25 pounds.

That "short quarter" fell out of use. Later the stone was introduced, but
almost only in Britain, changing the series to

1 ton = 20 cwt. = 20×4 quarters = 20×4×2 stones = 20×4×2×14 pounds.

The short units are closer to SI logic (2 and 5 based), but the long units
come closer to (more or less) even SI values.

--
A bus station is where a bus stops,
a train station is where a train stops,
on my desk I have a work station...

Markus Kuhn

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May 14, 2004, 12:31:23 PM5/14/04

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Jim Riley <jim...@pipeline.com> writes:
>>If your TI calculator doesn't have them, well then, blame TI. No one
>>ever said such functions would have to be on all calculators.
>
>There is no reason to assess blame. Markus Kuhn asserted that it was
>an extremely common feature to have a decimal shift capablity, which
>implies that it is extremely rare to not have the capability.

I must admit that after I did a reasonably careful comparison
of the usability of the functions of various scientific pocket
calculator brands about two decades ago, I decided that I really
liked what Casio is doing (algebraic parsing for +-*/^(), but stack-based
RPN operation for all other functions), and that on the other hand TI had a
user interface that I liked much less (with HP's pure RPN approach being in
a league of its own). The "ENG <-" and "ENG ->" keys on the Casios are just
one of the many features I loved. So I must admit that my view since then
has been somewhat restricted, as I have only ever bought and recommended
Casio calculators since then. In my mental model of the world,
"standard scientific pocket calculator" has become pretty much synonymous
with the user interface introduced by Casio. Their designers certainly
have carefully read and followed ISO 31.

Markus
(who sadly regrets that Casio has discontinued the very
much loved fx-451 with its fabulous 2-button unit conversion
function: http://www.livejournal.com/users/murkee/27725.html )

--
Markus Kuhn, Computer Laboratory, University of Cambridge
http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain

Christoph Paeper

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May 14, 2004, 2:47:28 PM5/14/04

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*Markus Kuhn* <n04W20...@cl.cam.ac.uk>:

>
> liked what Casio is doing (algebraic parsing for +-*/^(), but stack-based
> RPN operation for all other functions), and that on the other hand TI had a
> user interface that I liked much less

I agree for calculators with one line of display, but I'm now used to my
TI-30X IIS with its "EOS" input, i.e. like I learned to write calculations
down in school. That's not as fast, but less error prone, IMHO. It's just a
bit unhandy when inserting for instance a root operation in an existing
line, because you have to hit 2nd+DEL to activate insert mode for both "√("
and ")" (okay, in general I could just use ^½ instead).
I'd like it even more,
· if 2nd+π would offer me a selection of physical constants
· and 2nd+÷ was modulo,
· if it showed a thousands separator (ENG helps, though),
· if × and ÷ wouldn't be printed as * and /.

> The "ENG <-" and "ENG ->" keys on the Casios are just
> one of the many features I loved.

I've never used a calculator with such keys, but I suppose they just take up
space, because ×1000|÷1000 (or EE3) is quickly entered. I don't know whether
a display of SI prefixes would be better than ENG mode, but if cheaply
implementable as a fourth mode, why not. That could be misleading for area
and volume calculations, though.

--
Useless Fact #2:
Cat's urine glows under a blacklight.

Chris W

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May 15, 2004, 9:33:45 AM5/15/04

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If you want the best pocket scientific calculator take a look at this.

http://hp15c.org:8086

Chris W

Brian Inglis

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May 20, 2004, 1:07:32 PM5/20/04

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On Thu, 13 May 2004 20:51:35 +0200 in misc.metric-system, Christoph
Paeper <christop...@nurfuerspam.de> wrote:

>*Brian Inglis* <Brian....@SystematicSw.Invalid>:
>>
>> Whereas in the UK the US short (2000 lb) ton is relatively unknown.
>
>As far as I understand it, the Avoirdupois system, when introduced in
>Britain and its colonies, was
>
> 1 ton = 20 hundredweights = 20×4 quarters = 20×4×25 pounds.
>
>That "short quarter" fell out of use. Later the stone was introduced, but
>almost only in Britain, changing the series to
>
> 1 ton = 20 cwt. = 20×4 quarters = 20×4×2 stones = 20×4×2×14 pounds.
>
>The short units are closer to SI logic (2 and 5 based), but the long units
>come closer to (more or less) even SI values.

It's those factors of 7 and 11 that made the Imperial system what it
was: bloody annoying and confusing, but great for learning arithmetic!

Brian Inglis

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May 20, 2004, 1:45:27 PM5/20/04

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On Sat, 8 May 2004 21:54:51 +0000 (UTC) in misc.metric-system, "Jukka
K. Korpela" <jkor...@cs.tut.fi> wrote:

>"Paul Hobson" <gtg...@mail.gatech.edu> wrote:
>
>> I still think m/s on road signs is a bad idea. It's simply not
>> practical.
>
>What is practical depends greatly on habits and views.
>
>Once people thought it was practical to express the power of a car in
>horsepowers. This went on long after any comparison with the power of
>horse had lost all practical significance. (Besides, the horsepower was
>actually more than an average horse's power. But I digress.) People might
>still have said that the horsepower is practical and the watt (even when
>using the kilowatt) is simply not practical. But the only reason was that
>people were used to the old unit. It had to change sooner or later; the
>sooner the better. (Actually, I think there might even be countries where
>this change is still in progress.)
>
>> While driving over long distances, it's easier to think of
>> time in hours and then figure out how long it'll take given the
>> length in km (or miles) and your speed in km (or miles) per hour.
>
>Well, then start thinking of time in seconds and kiloseconds. :-)
>
>Seriously, if you think about 70 km/h for example, it may sound pretty
>slow, especially if you have long way to go and little time. Therefore,
>it is useful to think of it as about 19 m/s. That is, your car moves
>19 meters in a second. This should make you think about safety issues.
>How much can you, or your car, do in a second when something unexpected
>happens?

Actual travel takes some minutes for most journeys, or only a very few
hours at the most between stops, easily convertible to minutes.
With common speeds of 120, 90, 60 km/hr (and 30 in play/school zones)
you travel 2.0, 1.5, 1.0 km/min.
Conversion of distances in km to minutes of travel is extremely
trivial and useful.
Units of metres and seconds give numbers that are just too large for
many people to handle mentally, especially while driving.
Large numbers of hours are meaningless for long distance travel as
breaks, rest stops, and meals have then to be added onto the total.
So I'm pushing for total recalibration to km/min, or at least
equivalent multiples of km/hr, to limit the mental workload.