Metric System FAQ

Markus Kuhn

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Jun 19, 2004, 7:45:42 AM6/19/04

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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 mathematics 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, claimed that
teaching solely metric measurements could save an estimated 82
days of mathematics 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 can 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 (in air): 340 m/s

Speed of light (in air or vacuum): 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 speed of passenger planes: 600-800 km/h

Cruise altitude of passenger planes: 10 km

Official altitude boundary between Earth's
atmosphere and space ("Karman line"): 100 km

E) Temperatures

Lowest possible temperature: -273.15 °C = 0 K

Typical freezer temperature: -18 °C

Freezing water/melting ice: 0 °C

Drink with many ice cubes: 0 °C

Temperature of highest density of water: 4 °C

Typical refrigerator 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 (at sea level): 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
catalytic activity katal kat 1 kat = 1 mol/s

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?
----------------------------------------

The SI units whose symbols start with a capital letter are named after
the following scientists:

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

There has been at least one serious attempt to add a fictious
character to this list:

In many English-speaking countries, the digit 1 lacks an upstroke in
handwriting and is therefore difficult to distinguish from the letter
l. In the 1970s, the CGPM received suggestions to change the symbol of
the litre from the lowercase l to the uppercase L, to avoid such
confusion. This would of course violate the rule that only symbols
for units named after a person are capitalized in the SI, whereas the
word litre derives from the Greek and Latin root litra. It took not
long, before someone invented a hoax scientist, to help justify the
capital L. The April 1978 issue of "CHEM 13 NEWS", a newsletter for
Canadian high-school teachers, carried an article by Prof. Ken
A. Woolner (University of Waterloo), that elaborated on the made-up
biography of Claude Émile Jean-Baptiste Litre (1716-1778), an alleged
French pioneer in chemical glassware and volumetric measurement, son
of a family with a long tradition in wine-bottle manufacturing.
Details of this story have been compiled in

http://www.student.math.uwaterloo.ca/~stat231/stat231_01_02/w02/section3/fi1.2.pdf

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 = 10 m x 10 m
hectare ha 1 ha = 10000 m² = 100 m x 100 m

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,

Jun 20, 2004, 11:12:30 PM6/20/04

to

On Sat, 19 Jun 2004 11:45:42 +0000 (UTC), mg...@cl.cam.ac.uk (Markus
Kuhn) wrote:

> [The study "Education System
> Benefits of U.S. Metric Conversion", by Richard P. Phelps,
> published in Evaluation Review, February 1996, claimed that
> teaching solely metric measurements could save an estimated 82
> days of mathematics instruction-time annually, worth over 17
> billion dollars.]

Is the claim that 45% of mathematics instruction-time is devoted to
unit conversion skills?

> 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.

Why would there be an expectation that an educated person would know
by heart how to convert between gallons and cubic feet? How many
educated Europeans know by heart how to convert between liters and
cubic meters?

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

What is a traffic-calmed area?

> 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

What do you mean by "speed limit"?

> Comfortable office room temperature: 20-25 °C
>

> Hot day: 25-35 °C

Why are these specified in multiples of 5 degrees, and why do they
overlap?

> 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.

The SI standard is neutral as to whether "l" or "L" is used. The US
(NIST) has expressed a preference that the latter be used. "US
interpretation" would be better applied to the spelling of liter and
meter. I suggest:

Note: The use of either an uppercase L or a lowercase l as the symbol
for the litre was adopted by Resolution 6 of the 16th CGPM (1979).
Preference in the US is for use of an uppercase L so as to avoid
confusion with the numeral 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 SI Brochure (section 4.1) says that 1000 kg is a "tonne", but
notes that some English-speaking countries use the term "metric ton",
(the practice in the US). Searching the SI brochure, most of the
other references are to something called the "newton". Are they
related? Where is "ton" used for 1000 kg?

I would suggest:

mass tonne t 1 t = 1000 kg

Note: The tonne is called the "metric ton" in some English-speaking
countries.

--
Jim Riley

Erik Naggum

unread,

Jun 21, 2004, 12:15:32 AM6/21/04

to

* Jim Riley

> How many educated Europeans know by heart how to convert between
> liters and cubic meters?

Actually, all of them. If a European does not know this, s/he is not
educated. And I'm not making this up. I would be very surprised if
anyone I asked would be unable to figure out how to convert between
kilometers per hour to meters per second based solely on information
they already know. Attempts to ask people this have resulted in laughs
and surprises that that did indeed know when they thought about it. The
cubic centimeter is a common measure in engines, and it elicits the same
laugh and surprise when people are asked how to convert to milliliters.
Another rather obvious conversion is from millimeters of precipitation
to liters of water on a lawn: 1 mm of rain on 1 m² is 1 liter. People
tend to get an a-ha! moment out of this, because they extremely seldomly
make wrong guesses, and if they don't know, they'll figure it out when
they think about it. Stuff like this probably sounds like magic, but
over here in metric land, unit conversion really is a no-brainer.

--
Erik Naggum, Oslo, Norway | HTML mail is discarded unread | 2004-173

Act from reason, and failure makes you rethink and study harder.
Act from faith, and failure makes you blame someone and push harder.

Paul Hobson

unread,

Jun 21, 2004, 12:18:04 AM6/21/04

to

"Jim Riley" <jim...@pipeline.com> wrote in message
news:ymsBc.20439$Y3....@newsread2.news.atl.earthlink.net...

> On Sat, 19 Jun 2004 11:45:42 +0000 (UTC), mg...@cl.cam.ac.uk (Markus
> Kuhn) wrote:
>

>
> > 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.
>
> Why would there be an expectation that an educated person would know
> by heart how to convert between gallons and cubic feet? How many
> educated Europeans know by heart how to convert between liters and
> cubic meters?

I think the fact that everything is based on powers of ten and that 1 mL is
also a cubic centimeter, converting between liters and cubic meters is much
more intuitive and references aren't necessarily required.

>
> > Speed limit in traffic-calmed areas: 30 km/h
>
> What is a traffic-calmed area?
>
> > 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
>
> What do you mean by "speed limit"?

You know, the speed limit...the maximum legal speed one can drive an
automobile on a road.

> > Comfortable office room temperature: 20-25 °C
> >
> > Hot day: 25-35 °C
>
> Why are these specified in multiples of 5 degrees, and why do they
> overlap?

It's easier to remember 20-25 than 22-26. In the US, meterologists on TV
say, "It'll be in the seventies." Since a change of one degree C represents
more of a change in temperature than a change of 1 degree F, it makes sense
to sut the margins down to the next convenient size.

> > 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.
>
> The SI standard is neutral as to whether "l" or "L" is used. The US
> (NIST) has expressed a preference that the latter be used. "US
> interpretation" would be better applied to the spelling of liter and
> meter. I suggest:
>
> Note: The use of either an uppercase L or a lowercase l as the symbol
> for the litre was adopted by Resolution 6 of the 16th CGPM (1979).
> Preference in the US is for use of an uppercase L so as to avoid
> confusion with the numeral 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 SI Brochure (section 4.1) says that 1000 kg is a "tonne", but
> notes that some English-speaking countries use the term "metric ton",
> (the practice in the US). Searching the SI brochure, most of the
> other references are to something called the "newton". Are they
> related? Where is "ton" used for 1000 kg?

A newton is the SI unit of force (analogous to pounds). A mass of 1 kg has
a weight on Earth of 9.81 N.

Note: Since F=ma where F is force, m mass and a acceleration (due to gravity
above), Newtons are equal to kg*m/s^2

Shawn K. Quinn

unread,

Jun 21, 2004, 1:25:45 AM6/21/04

to

Jim Riley wrote:

> On Sat, 19 Jun 2004 11:45:42 +0000 (UTC), mg...@cl.cam.ac.uk (Markus
> Kuhn) wrote:
>> Speed limit in traffic-calmed areas: 30 km/h
>
> What is a traffic-calmed area?

Neighborhood streets or similar areas not designed for significant volumes
of thru traffic.

>> 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
>
> What do you mean by "speed limit"?

I'd say it's the same definition that you'd think it is.

Many rural roads are signed for 55 mi/h (88 km/h) or higher, at least in
Texas. Many urban roads, particularly in suburban areas, are signed for 40
or 45 mi/h (64 or 72 km/h) around here.

>> Comfortable office room temperature: 20-25 °C
>>
>> Hot day: 25-35 °C
>
> Why are these specified in multiples of 5 degrees, and why do they
> overlap?

25 degrees Celsius corresponds to 77 degrees Fahrenheit, and while that
might be pushing the limit of "comfortable office room temperature" it
should be tolerable. I'd say 30 degrees Celsius (corresponding to 86
degrees Fahrenheit) would be a more reasonable lower bound for "hot day".

--
Shawn K. Quinn

Gene Nygaard

unread,

Jun 21, 2004, 7:12:26 AM6/21/04

to

On Mon, 21 Jun 2004 03:12:30 GMT, Jim Riley <jim...@pipeline.com>
wrote:

>On Sat, 19 Jun 2004 11:45:42 +0000 (UTC), mg...@cl.cam.ac.uk (Markus
>Kuhn) wrote:
>
>> [The study "Education System
>> Benefits of U.S. Metric Conversion", by Richard P. Phelps,
>> published in Evaluation Review, February 1996, claimed that
>> teaching solely metric measurements could save an estimated 82
>> days of mathematics instruction-time annually, worth over 17
>> billion dollars.]
>
>Is the claim that 45% of mathematics instruction-time is devoted to
>unit conversion skills?
>
>
>> 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.
>
>Why would there be an expectation that an educated person would know
>by heart how to convert between gallons and cubic feet? How many
>educated Europeans know by heart how to convert between liters and
>cubic meters?

Almost all.

>> Speed limit in traffic-calmed areas: 30 km/h
>
>What is a traffic-calmed area?
>
>> 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
>
>What do you mean by "speed limit"?
>
>
>> Comfortable office room temperature: 20-25 °C
>>
>> Hot day: 25-35 °C
>
>Why are these specified in multiples of 5 degrees, and why do they
>overlap?
>

>> volume litre l, L 1 l = 1 dmł

>> 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.
>
>The SI standard is neutral as to whether "l" or "L" is used. The US
>(NIST) has expressed a preference that the latter be used. "US
>interpretation" would be better applied to the spelling of liter and
>meter. I suggest:
>
> Note: The use of either an uppercase L or a lowercase l as the symbol
> for the litre was adopted by Resolution 6 of the 16th CGPM (1979).
> Preference in the US is for use of an uppercase L so as to avoid
> confusion with the numeral 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 SI Brochure (section 4.1) says that 1000 kg is a "tonne", but
>notes that some English-speaking countries use the term "metric ton",
>(the practice in the US). Searching the SI brochure, most of the
>other references are to something called the "newton".

Only through F=ma in conjunction with some known acceleration. Those
newtons are units of force. The metric tons acceptable for use with
SI are not.

There used to be metric tons force as well (just as there are short
tons force in the U.S., and long tons force in the U.K. as well as the
normal units of mass; but long tons in the U.S. are always and short
tons in the U.S. are usually mass units, and the short tons have
largely disappeared from U.K. usage even as mass units). But it is
only the tonne or metric ton as a unit of mass which is acceptable for
use with SI; the metric ton force (those obsolete units were directly
related to the newton, equal to 9.80665 kN exactly) is not acceptable
for use with SI.

>Are they
>related? Where is "ton" used for 1000 kg?

In the U.S., for one place. Note also that "tonne" is the general
term in French, just as ambiguous as "ton" in English. For example,
what do you suppose an unidentified "tonne" would likely have meant in
Quebec 50 years ago? Most likely a "tonne courte," or a "tonne forte"
in the context of ocean shipping, and not likely a "tonne mčtrique."

Even in English, the word "tonne" is ambiguous enough that many people
fell the need to make the distinction:

Google "metric tonnes": about 58,500 hits
Google "metric tonne": about 14,000 hits
Google "short tonnes": about 272 hits
Google "short tonne": about 85 hits
Google "long tonnes": about 203 hits
Google "long tonne": about 33 hits

>I would suggest:
>
> mass tonne t 1 t = 1000 kg
>
> Note: The tonne is called the "metric ton" in some English-speaking
> countries.

A more useful change would be an explicit listing that 1 t = 1 Mg, or
better yet an expression of the same thing in words. Using the SI
unit avoids all that ambiguity of the words "ton" and "tonne."

Gene Nygaard

Markus Kuhn

unread,

Jun 21, 2004, 10:58:47 AM6/21/04

to

Jim Riley <jim...@pipeline.com> writes:
>> Speed limit in traffic-calmed areas: 30 km/h
>What is a traffic-calmed area?

Plenty of examples of US implementations of these are on

http://www.state.de.us/research/register/september2000/signing%20and%20marking.revised---V-1.htm

>> 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
>
>What do you mean by "speed limit"?

The numbers are meant to represent typical legal maximum
speeds allowed on various types of roads in a large number of
countries. This is not meant to be a comprehensive list of
speed limits (for example, there are indeed some countries
with a highway speed limit of 250 km/h, 300000 km/s or
infinity, depending on your exact interpretation of all
applicable laws :-).

>
>> Comfortable office room temperature: 20-25 °C
>>
>> Hot day: 25-35 °C
>
>Why are these specified in multiples of 5 degrees, and why do they
>overlap?

The length of the overlaping interval is zero, and the multiples
of 5 are not only convenient to remember (which is the sole
purpose of this list), but actually match published in-door climate
comfort curves (recommended office temperatures) at about 50%
relative humidity rather well (±1 °C) and fall within their
error bars.

Markus

Andreas Prilop

unread,

Jun 21, 2004, 11:52:58 AM6/21/04

to

On Sat, 19 Jun 2004, Markus Kuhn wrote:

> Lines: 1887

>
> Suggestions for improvement are welcome!

Which other newsgroup has a FAQ of 1887 lines posted to Usenet?
Please restrict the Usenet FAQ to a reasonable length and
include a URL to the complete version.

Thank you!

Philip Kendall

unread,

Jun 21, 2004, 11:59:38 AM6/21/04

to

In article <Pine.GSO.4.44.0406211748050.12363-100000@s5b003>,

Andreas Prilop <nhtc...@rrzn-user.uni-hannover.de> wrote:
>On Sat, 19 Jun 2004, Markus Kuhn wrote:
>
>> Lines: 1887
>>
>> Suggestions for improvement are welcome!
>
>Which other newsgroup has a FAQ of 1887 lines posted to Usenet?

comp.lang.c

Cheers,

Phil

--
Philip Kendall <pa...@srcf.ucam.org>
http://www.srcf.ucam.org/~pak21/

Markus Kuhn

unread,

Jun 21, 2004, 4:31:24 PM6/21/04

to

In article <Pine.GSO.4.44.0406211748050.12363-100000@s5b003>,

I could also split it up into three parts if that helps.

Fully posting the FAQ seems to elicit far more response, as
people find it far easier to follow-up and quote.

Markus

Erik Naggum

unread,

Jun 21, 2004, 11:31:07 PM6/21/04

to

* Jim Riley

> Why would there be an expectation that an educated person would know
> by heart how to convert between gallons and cubic feet? How many
> educated Europeans know by heart how to convert between liters and
> cubic meters?

In http://www.truthout.org/environment.shtml we find a new unit I had
not yet encountered.

The report said the drought has produced the lowest flow in the
Colorado River on record, with an adjusted annual average flow
of only 5.4 million acre-feet at Lees Ferry, Arizona, during the
period 2001-2003. By comparison, during the Dust Bowl years,
between 1930 and 1937, the annual flow averaged about 10.2
million acre-feet, the report said.

Of course, the only useful thing to know here is the relative amounts
and there is absolutely no value to the regular reader to calculate
exactly how much water-flow an acre-feet per year is. It's just *a lot*
of water. In metric terms, it's close to 1233.5 mł/yr or 1.2335 ML/yr.

However, 1 million acre-feet is close to 1.2335 kmł. I can actually
relate to 1 kmł intuitively, but an annual average flow of this kind of
volume is close to 39.1 mł/s, which is a very intuitive unit to me, not
only because I can easily imagine it, but because the flow from water
reservoirs in Norway is reported in this unit.

The numbers are thus

5.4 million acre-feet per year ~= 211.1 mł/s
10.2 million acre-feet per year ~= 398.7 mł/s

Now I can relate to the average of 2.8 mł/s output from Oslo's water
reservoirs...

--
Erik Naggum, Oslo, Norway | HTML mail is discarded unread | 2004-174

Irrwahn Grausewitz

unread,

Jun 22, 2004, 6:10:39 AM6/22/04

to

No, please don't. It's rather convenient to have the most
recent version of the FAQ posted to the group. People
unwilling to retrieve long messages in general should
configure their news reader software accordingly, anyway.

Regards
--
Irrwahn
(irrw...@freenet.de)

Irrwahn Grausewitz

unread,

Jun 22, 2004, 7:54:33 AM6/22/04

to

Irrwahn Grausewitz <irrw...@freenet.de> wrote:
>Andreas Prilop <nhtc...@rrzn-user.uni-hannover.de> wrote:
>>On Sat, 19 Jun 2004, Markus Kuhn wrote:
>>
>>> Lines: 1887
>>>
>>> Suggestions for improvement are welcome!
>>
>>Which other newsgroup has a FAQ of 1887 lines posted to Usenet?

BTW, the comp.lang.c FAQ has 6929 lines, and I can't remember
anyone ever complained.

<snip>
--
Irrwahn
(irrw...@freenet.de)

Dr John Stockton

unread,

Jun 22, 2004, 7:18:20 PM6/22/04

to

JRS: In article <rk0gd0dvv2qgojg1d...@4ax.com>, seen in
news:misc.metric-system, Irrwahn Grausewitz <irrw...@freenet.de>
posted at Tue, 22 Jun 2004 12:10:39 :

I find it inconveniently large.

It is posted monthly. If it were split into four parts posted weekly,
with each part prefixed by a copy of the communal index, then it would
not seem so large.

More importantly, I suspect that, done thusly, more of us would glance
through or review the whole of each posting, which would lead to more,
and perhaps better, feedback.

It should be easy enough to use software to convert whatever form is
most conveniently edited to whatever forms are actually published; also
to mark up where changes have occurred.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME. ©
Web <URL:http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, & links.
Proper <= 4-line sig. separator as above, a line exactly "-- " (SonOfRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "> " (SonOfRFC1036)

Jim Riley

unread,

Jun 22, 2004, 9:16:17 PM6/22/04

to

On 21 Jun 2004 14:58:47 GMT, n04W26...@cl.cam.ac.uk (Markus Kuhn)
wrote:

>Jim Riley <jim...@pipeline.com> writes:
>>> Speed limit in traffic-calmed areas: 30 km/h
>>What is a traffic-calmed area?
>
>Plenty of examples of US implementations of these are on
> http://www.state.de.us/research/register/september2000/signing%20and%20marking.revised---V-1.htm

Most people don't read legal registers. Delaware claims to have the
first statewide traffic calming manual in the country, published in
2000. The source that you gave above gives a design speed of 40 kph
for speed humps, 48 kph for speed tables, and a maximum of 48 kph for
traffic circles. Street closures restrict traffic to 0 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
>>
>>What do you mean by "speed limit"?
>
>The numbers are meant to represent typical legal maximum
>speeds allowed on various types of roads in a large number of
>countries.

Which countries? Given the purpose of this section (e.g. how fast
people walk, bicycles, etc.), what purpose is served by using a legal
definition for car speeds? Terms like "road" are rather ill-defined.

>>> Comfortable office room temperature: 20-25 °C
>>>
>>> Hot day: 25-35 °C
>>
>>Why are these specified in multiples of 5 degrees, and why do they
>>overlap?
>
>The length of the overlaping interval is zero, and the multiples
>of 5 are not only convenient to remember (which is the sole
>purpose of this list), but actually match published in-door climate
>comfort curves (recommended office temperatures) at about 50%
>relative humidity rather well (±1 °C) and fall within their
>error bars.

Does this mean that the recommended upper limit is 24 °C or 26 °C?

Are there any similar standards for hot days?

--
Jim Riley

Jim Riley

unread,

Jun 22, 2004, 9:26:17 PM6/22/04

to

On Mon, 21 Jun 2004 00:18:04 -0400, "Paul Hobson"
<gtg...@mail.gatech.edu> wrote:

>"Jim Riley" <jim...@pipeline.com> wrote in message
>news:ymsBc.20439$Y3....@newsread2.news.atl.earthlink.net...

>> Why would there be an expectation that an educated person would know

>> by heart how to convert between gallons and cubic feet? How many
>> educated Europeans know by heart how to convert between liters and
>> cubic meters?
>
>I think the fact that everything is based on powers of ten and that 1 mL is
>also a cubic centimeter, converting between liters and cubic meters is much
>more intuitive and references aren't necessarily required.

Knowing by heart would imply that you you would not need intuition.

>> What do you mean by "speed limit"?
>
>You know, the speed limit...the maximum legal speed one can drive an
>automobile on a road.

I thought it odd to combine typical speeds to walking and bicycling
with legal limits.

>> > Comfortable office room temperature: 20-25 °C
>> >
>> > Hot day: 25-35 °C
>>
>> Why are these specified in multiples of 5 degrees, and why do they
>> overlap?
>
>It's easier to remember 20-25 than 22-26. In the US, meterologists on TV
>say, "It'll be in the seventies."

As in "it'll be a real scorcher tomorrow with the high in the mid
70's"?

>A newton is the SI unit of force (analogous to pounds). A mass of 1 kg has
>a weight on Earth of 9.81 N.

I'm sorry. I was amused that a search of the SI brochure for "ton"
brought up "tonne", "metric ton", and a "new ton".

--
Jim Riley

Jim Riley

unread,

Jun 22, 2004, 9:31:07 PM6/22/04

to

On Mon, 21 Jun 2004 00:25:45 -0500, "Shawn K. Quinn"
<skq...@xevious.kicks-ass.net> wrote:

>Jim Riley wrote:
>> What do you mean by "speed limit"?
>
>I'd say it's the same definition that you'd think it is.
>
>Many rural roads are signed for 55 mi/h (88 km/h) or higher, at least in
>Texas. Many urban roads, particularly in suburban areas, are signed for 40
>or 45 mi/h (64 or 72 km/h) around here.

It sounds like different areas have different understanding of the
term "road".

>>> Comfortable office room temperature: 20-25 °C
>>>
>>> Hot day: 25-35 °C
>>
>> Why are these specified in multiples of 5 degrees, and why do they
>> overlap?
>
>25 degrees Celsius corresponds to 77 degrees Fahrenheit, and while that
>might be pushing the limit of "comfortable office room temperature" it
>should be tolerable. I'd say 30 degrees Celsius (corresponding to 86
>degrees Fahrenheit) would be a more reasonable lower bound for "hot day".

Agreed.

--
Jim Riley

Jim Riley

unread,

Jun 22, 2004, 9:46:56 PM6/22/04

to

On Mon, 21 Jun 2004 06:12:26 -0500, Gene Nygaard <gnyg...@nccray.com>
wrote:

>On Mon, 21 Jun 2004 03:12:30 GMT, Jim Riley <jim...@pipeline.com>
>wrote:

>>Are they

>>related? Where is "ton" used for 1000 kg?
>
>In the U.S., for one place.

It is a "metric ton" in the US.

>>I would suggest:
>>
>> mass tonne t 1 t = 1000 kg
>>
>> Note: The tonne is called the "metric ton" in some English-speaking
>> countries.
>
>A more useful change would be an explicit listing that 1 t = 1 Mg, or
>better yet an expression of the same thing in words. Using the SI
>unit avoids all that ambiguity of the words "ton" and "tonne."

This is in a section of the FAQ dealing with the units which are not
part of the SI, but accepted for use with the SI. The SI brochure
uses a definition of 1000 kg for the tonne, and notes that "metric
ton" is used in some English-speaking companies.

--
Jim Riley

Gene Nygaard

unread,

Jun 22, 2004, 11:54:56 PM6/22/04

to

On Wed, 23 Jun 2004 01:46:56 GMT, Jim Riley <jim...@pipeline.com>
wrote:

>On Mon, 21 Jun 2004 06:12:26 -0500, Gene Nygaard <gnyg...@nccray.com>
>wrote:
>
>>On Mon, 21 Jun 2004 03:12:30 GMT, Jim Riley <jim...@pipeline.com>
>>wrote:
>
>>>Are they
>>>related? Where is "ton" used for 1000 kg?
>>
>>In the U.S., for one place.
>
>It is a "metric ton" in the US.

http://www.usaid.gov/press/releases/2001/pr011217.html
U.S. Government Sends 115,000 Tons of Wheat to Afghan People

http://www.fas.usda.gov/info/factsheets/cuba/wheat.html
Cuba is the largest importer of wheat and wheat products in the
Caribbean, taking virtually all of its 1 million tons per year of
imports from the European Union (EU).

http://www.artukraine.com/agrinews/usda.htm
According to the January forecast by the US Department of Agriculture,
in Washington, D.C. Ukraine will likely move from third to fourth
place among the world's largest exporters of wheat as Russia's exports
of wheat are projected to increase from 7.5 million tons, to 9.5 M.
tons, ProAgro sources told Ukrinform.

http://www.chron.com/cs/CDA/ssistory.mpl/special/iraq/1828629
The United States is sending 200,000 tons of wheat and rice to Iraq,
Agriculture Secretary Ann Veneman said today

http://www.grains.org/news/latest_news/increased_demand_for_us_corn.html
In Russia, a poor harvest has left the wet milling industry short
200,000 tons of corn, according to director Alexander Kholopov.

outside the U.S.A
------------------
http://www.slovak.sk/magazin_slovakia/496_Slovakia/economic_news/regulation.htm
Some 912 thousand tons of cereals still remained without a buyer on
July 12, and in consequence the State Market Regulation Fund decided
to step in to remedy the situation.

http://www.dailytimes.com.pk/default.asp?page=story_11-6-2004_pg7_51
Deputy Director Arif Raza Bukhari said the procurement centres in the
six districts of the former Multan division had 7,000 tons of wheat,
indicating that the pace of the purchase had been slow.

http://english.pravda.ru/cis/2002/07/20/32907.html
Russian border guards, who are stationed in Tajikistan, ferried 48
tons of wheat into neighbouring Afghanistan the other day. Such wheat
is ear-marked for the northern Afghan population in line with a UN
humanitarian-aid program.

http://www.manilatimes.net/national/2004/jun/02/yehey/prov/20040602pro4.html
Of the total production of 205,585 tons, the harvest from the first
crop (January to March) came from 151,604 ha., or 73.7 percent. The
yellow corn harvest reached a total 134,819 tons, or 88.9 percent of
the 151,604 tons, while white corn yielded 16,785 tons, or 11.1
percent.

>>>I would suggest:
>>>
>>> mass tonne t 1 t = 1000 kg
>>>
>>> Note: The tonne is called the "metric ton" in some English-speaking
>>> countries.
>>
>>A more useful change would be an explicit listing that 1 t = 1 Mg, or
>>better yet an expression of the same thing in words. Using the SI
>>unit avoids all that ambiguity of the words "ton" and "tonne."
>
>This is in a section of the FAQ dealing with the units which are not
>part of the SI, but accepted for use with the SI. The SI brochure
>uses a definition of 1000 kg for the tonne, and notes that "metric
>ton" is used in some English-speaking companies.

My point is specifically pointing out the simple exchange of words
with no change in the number would help eliminate the confusing
ambiguities. Metric tons may be _acceptable_ for use with SI; that
doesn't mean they are on equal footing, and shouldn't be discouraged.

Gene Nygaard

Bob

unread,

Jun 22, 2004, 11:54:28 PM6/22/04

to

On Wed, 23 Jun 2004 00:18:20 +0100, Dr John Stockton
<sp...@merlyn.demon.co.uk> wrote:

>>>
>>>Which other newsgroup has a FAQ of 1887 lines posted to Usenet?
>>>Please restrict the Usenet FAQ to a reasonable length and
>>>include a URL to the complete version.
>>
>>No, please don't. It's rather convenient to have the most
>>recent version of the FAQ posted to the group. People
>>unwilling to retrieve long messages in general should
>>configure their news reader software accordingly, anyway.
>
>I find it inconveniently large.
>

then don't DL it.

>It is posted monthly. If it were split into four parts posted weekly,
>with each part prefixed by a copy of the communal index, then it would
>not seem so large.
>

It may not _seem_ so large, but it would actually be larger, since
there are about 4 1/3 weeks per month.

In general, I am not a fan of long posts -- partly because it often
means they are just poorly trimmed. But the FAQ for a new group would
seem to be a special case, at least for a while.

(In sci.chem, a rather long FAQ is posted from time to time. It is
done all at once, but broken down into several shorter messages.)

bob

Jim Riley

unread,

Jun 24, 2004, 8:35:28 PM6/24/04

to

On Tue, 22 Jun 2004 22:54:56 -0500, Gene Nygaard <gnyg...@nccray.com>
wrote:

>On Wed, 23 Jun 2004 01:46:56 GMT, Jim Riley <jim...@pipeline.com>
>wrote:
>
>>On Mon, 21 Jun 2004 06:12:26 -0500, Gene Nygaard <gnyg...@nccray.com>
>>wrote:
>>
>>>On Mon, 21 Jun 2004 03:12:30 GMT, Jim Riley <jim...@pipeline.com>
>>>wrote:
>>
>>>>Are they
>>>>related? Where is "ton" used for 1000 kg?
>>>
>>>In the U.S., for one place.
>>
>>It is a "metric ton" in the US.
>
>http://www.usaid.gov/press/releases/2001/pr011217.html
>U.S. Government Sends 115,000 Tons of Wheat to Afghan People

Headline does not usage in article.

>http://www.fas.usda.gov/info/factsheets/cuba/wheat.html
>Cuba is the largest importer of wheat and wheat products in the
>Caribbean, taking virtually all of its 1 million tons per year of
>imports from the European Union (EU).

Unclear which units are used.

>http://www.artukraine.com/agrinews/usda.htm
>According to the January forecast by the US Department of Agriculture,
>in Washington, D.C. Ukraine will likely move from third to fourth
>place among the world's largest exporters of wheat as Russia's exports
>of wheat are projected to increase from 7.5 million tons, to 9.5 M.
>tons, ProAgro sources told Ukrinform.

My quick impression is that "artukraine.com" is more focused on
cultural affairs (though wheat production may have deep cultural
implications for the Ukraine).

Source material from USDA estimate uses metric ton (or 1000s of metric
tons) in tables (and "tons" in text).

http://www.fas.usda.gov/grain/circular/2003/01-03/graintoc.htm

>http://www.chron.com/cs/CDA/ssistory.mpl/special/iraq/1828629
> The United States is sending 200,000 tons of wheat and rice to Iraq,
>Agriculture Secretary Ann Veneman said today

This was an AP wire service report published in the _Houston
Chronicle_ The press release from USAID uses "metric ton" in first
usage, and "ton" in subsequent usage.

http://www.usaid.gov/press/releases/2003/pr030321.html

Agriculture Secretary Ann M. Veneman and Agency for International
Development Administrator Andrew S. Natsios announced the immediate
release of 200,000 metric tons of wheat from the Bill Emerson
Humanitarian Trust, with another 400,000 tons to be made available as
needed.

>http://www.grains.org/news/latest_news/increased_demand_for_us_corn.html
>In Russia, a poor harvest has left the wet milling industry short
>200,000 tons of corn, according to director Alexander Kholopov.

This press release uses metric tons throughout, with the exception fo
a couple of paraphrases such as these. Note that the articles that
you have cites are related to world market. The standard contract on
the Chicago Board of Trade for wheat is 5000 bushels.

The following based on USDA forecasts mixes bushels (for US
production) and mmt (million metric tons) for non-US production.

http://www.cbot.com/cbot/docs/48372.pdf

>>>>I would suggest:
>>>>
>>>> mass tonne t 1 t = 1000 kg
>>>>
>>>> Note: The tonne is called the "metric ton" in some English-speaking
>>>> countries.
>>>
>>>A more useful change would be an explicit listing that 1 t = 1 Mg, or
>>>better yet an expression of the same thing in words. Using the SI
>>>unit avoids all that ambiguity of the words "ton" and "tonne."
>>
>>This is in a section of the FAQ dealing with the units which are not
>>part of the SI, but accepted for use with the SI. The SI brochure
>>uses a definition of 1000 kg for the tonne, and notes that "metric
>>ton" is used in some English-speaking companies.
>
>My point is specifically pointing out the simple exchange of words
>with no change in the number would help eliminate the confusing
>ambiguities. Metric tons may be _acceptable_ for use with SI; that
>doesn't mean they are on equal footing, and shouldn't be discouraged.

I'm sorry, I do not understand what you are trying to say. Let's
start over.

The FAQ currently reads (please see FAQ for context):

mass ton t 1 t = 1000 kg

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.

I suggested that this be changed to:

mass tonne t 1 t = 1000 kg

Note: The tonne is called the "metric ton" in some English-speaking
countries.

What specifically are you suggesting?

--
Jim Riley

Gene Nygaard

unread,

Jun 24, 2004, 11:33:48 PM6/24/04

to

On Fri, 25 Jun 2004 00:35:28 GMT, Jim Riley <jim...@pipeline.com>
wrote:

>On Tue, 22 Jun 2004 22:54:56 -0500, Gene Nygaard <gnyg...@nccray.com>
>wrote:
>
>>On Wed, 23 Jun 2004 01:46:56 GMT, Jim Riley <jim...@pipeline.com>
>>wrote:
>>
>>>On Mon, 21 Jun 2004 06:12:26 -0500, Gene Nygaard <gnyg...@nccray.com>
>>>wrote:
>>>
>>>>On Mon, 21 Jun 2004 03:12:30 GMT, Jim Riley <jim...@pipeline.com>
>>>>wrote:
>>>
>>>>>Are they
>>>>>related? Where is "ton" used for 1000 kg?
>>>>
>>>>In the U.S., for one place.
>>>
>>>It is a "metric ton" in the US.
>>
>>http://www.usaid.gov/press/releases/2001/pr011217.html
>>U.S. Government Sends 115,000 Tons of Wheat to Afghan People
>
>Headline does not usage in article.
>
>>http://www.fas.usda.gov/info/factsheets/cuba/wheat.html
>>Cuba is the largest importer of wheat and wheat products in the
>>Caribbean, taking virtually all of its 1 million tons per year of
>>imports from the European Union (EU).
>
>Unclear which units are used.

Not to anybody in the industry it isn't unclear.

>>http://www.artukraine.com/agrinews/usda.htm
>>According to the January forecast by the US Department of Agriculture,
>>in Washington, D.C. Ukraine will likely move from third to fourth
>>place among the world's largest exporters of wheat as Russia's exports
>>of wheat are projected to increase from 7.5 million tons, to 9.5 M.
>>tons, ProAgro sources told Ukrinform.
>
>My quick impression is that "artukraine.com" is more focused on
>cultural affairs (though wheat production may have deep cultural
>implications for the Ukraine).
>
>Source material from USDA estimate uses metric ton (or 1000s of metric
>tons) in tables (and "tons" in text).

As you are discovering, the tons aren't always identified. I could
come up with a few hundred more examples, many from newspapers and
magazines as well as the internet.

>http://www.fas.usda.gov/grain/circular/2003/01-03/graintoc.htm
>
>>http://www.chron.com/cs/CDA/ssistory.mpl/special/iraq/1828629
>> The United States is sending 200,000 tons of wheat and rice to Iraq,
>>Agriculture Secretary Ann Veneman said today
>
>This was an AP wire service report published in the _Houston
>Chronicle_ The press release from USAID uses "metric ton" in first
>usage, and "ton" in subsequent usage.
>
>http://www.usaid.gov/press/releases/2003/pr030321.html
>
>Agriculture Secretary Ann M. Veneman and Agency for International
>Development Administrator Andrew S. Natsios announced the immediate
>release of 200,000 metric tons of wheat from the Bill Emerson
>Humanitarian Trust, with another 400,000 tons to be made available as
>needed.

So what would you conclude--that the first ones are identified because
they are different from the tons which don't need to be identified in
the second instance?

>>http://www.grains.org/news/latest_news/increased_demand_for_us_corn.html
>>In Russia, a poor harvest has left the wet milling industry short
>>200,000 tons of corn, according to director Alexander Kholopov.
>
>This press release uses metric tons throughout, with the exception fo
>a couple of paraphrases such as these. Note that the articles that
>you have cites are related to world market. The standard contract on
>the Chicago Board of Trade for wheat is 5000 bushels.

That's one reason we know that those tons used in relation to
production of grains are not short tons, nor are they long tons. They
are metric tons, whether they are identified as such as the often are,
or whether they are not as also happens very often.

1 t = 1 Mg

which makes it quite clear that it can be expressed just as simply in
SI units, without having to add additional zeros at the end.

It could be 1 t = 1000 kg = 1 Mg

Also helpful, something that could be but not necessarily something
I'd claim _should_ be in the faq, would be

1 000 t = 1 Gg
1 000 000 t (often "million metric tons" in newspapers and the like) =
1 Tg

Gene Nygaard

Michael Dahms

unread,

Jun 25, 2004, 1:21:29 AM6/25/04

to

Jim Riley wrote:

> The FAQ currently reads (please see FAQ for context):
>
> mass ton t 1 t = 1000 kg
>
> 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.
>
> I suggested that this be changed to:
>
> mass tonne t 1 t = 1000 kg
>
> Note: The tonne is called the "metric ton" in some English-speaking
> countries.

AFAIK, 'ton' ist the SI-word for 1000 kg.

Michael Dahms

Markus Kuhn

unread,

Jun 25, 2004, 5:39:45 AM6/25/04

to

Jim Riley <jim...@pipeline.com> writes:
>The FAQ currently reads (please see FAQ for context):
>
> mass ton t 1 t = 1000 kg
>
> 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.
>
>I suggested that this be changed to:
>
> mass tonne t 1 t = 1000 kg
>
> Note: The tonne is called the "metric ton" in some English-speaking
> countries.
>

Considering that ISO 31 and ISO 1000 also write "tonne" consistently,
I have just changed the FAQ to

mass tonne t 1 t = 1000 kg

Note: The tonne (1000 kg) is commonly also called just "ton". The term
"metric ton" is frequently used in some English-speaking countries for
1000 kg, to avoid confusion with other tons still in use there (in
particular, in the US there is a "short ton" of 907.18474 kg and a
"long ton" of 1016.046909 kg).

http://www.cl.cam.ac.uk/~mgk25/metric-system-faq.txt

Once US has become fully metric, I have no doubt that
the terms "metric ton" and "tonne" will rapidly collapse
into the shorter and then unambiguous "ton" for 1000 kg
in the English language.

(I found it always odd that the Star Trek authors assume,
that people will still be saying "metric ton" in the
24th century.)

Markus

Joona I Palaste

unread,

Jun 25, 2004, 5:53:18 AM6/25/04

to

Markus Kuhn <n04W26...@cl.cam.ac.uk> scribbled the following:

> (I found it always odd that the Star Trek authors assume,
> that people will still be saying "metric ton" in the
> 24th century.)

Have you read many Star Trek books? I have, almost half of all TNG books
ever written. And I can tell you that not only do they say "metric ton"
in the 24th century, they routinely still use inches, feet, miles,
ounces, pounds, etc. This *in conjunction* with metric units. Authors
switch from one unit system to another at random.

--
/-- Joona Palaste (pal...@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"As a boy, I often dreamed of being a baseball, but now we must go forward, not
backward, upward, not forward, and always whirling, whirling towards freedom!"
- Kang

DWT

unread,

Jun 25, 2004, 9:54:03 AM6/25/04

to

n04W26...@cl.cam.ac.uk (Markus Kuhn) wrote in
<cbgrt1$7t$1...@pegasus.csx.cam.ac.uk>:

| Once US has become fully metric, I have no doubt that
| the terms "metric ton" and "tonne" will rapidly collapse
| into the shorter and then unambiguous "ton" for 1000 kg
| in the English language.

Do you actually believe the US will ever become fully metric, Markus, or
are you using that in the sense that once the US has become fully metric,
donkeys will fly and people will walk on their eyelashes?

I for one have no hope of its happening. Like my becoming a billionaire
(even by the US definition of "billion"), it's something I'd like to see
but won't.

--
David W. Tamkin

The reply address is bluelighted through midnight (UT -0500) on 02Jul2004.

Uwe Hercksen

unread,

Jun 25, 2004, 11:01:28 AM6/25/04

to

Markus Kuhn schrieb:

>
> Considering that ISO 31 and ISO 1000 also write "tonne" consistently,
> I have just changed the FAQ to
>
> mass tonne t 1 t = 1000 kg
>
> Note: The tonne (1000 kg) is commonly also called just "ton". The term
> "metric ton" is frequently used in some English-speaking countries for
> 1000 kg, to avoid confusion with other tons still in use there (in
> particular, in the US there is a "short ton" of 907.18474 kg and a
> "long ton" of 1016.046909 kg).
>

Hello,

instead of using this sequence: kilotonne, tonne, kilogram, gram,
milligram, microgram...
it would be more consequent to use: gigagram, megagram, kilogram, gram,
milligram, microgram...
It is easy using the SI prefixes to write the mass of the earth, it is
5976 yottagram, we need another prefix for 1000 yottas. But when think
of the sun, we should have three more prefixes for 1.989*10^30 kg.

Bye

Domilare

unread,

Jun 25, 2004, 1:13:29 PM6/25/04

to

"DWT" <nobody@[127.0.0.1]> a écrit dans le message de
news:cbhapr$6ac$1...@panix3.panix.com...

> n04W26...@cl.cam.ac.uk (Markus Kuhn) wrote in
> <cbgrt1$7t$1...@pegasus.csx.cam.ac.uk>:
>
> | Once US has become fully metric, I have no doubt that
> | the terms "metric ton" and "tonne" will rapidly collapse
> | into the shorter and then unambiguous "ton" for 1000 kg
> | in the English language.
>
> Do you actually believe the US will ever become fully metric, Markus,

<. . . . . .>

This reader at least is positive that the US will become fully metric.

It may take more time than he has, though (as he is born in the first third
of last century)

Greetings

Dominique Larré

Markus Kuhn

unread,

Jun 25, 2004, 4:27:46 PM6/25/04

to

Joona I Palaste <pal...@cc.helsinki.fi> writes:
>Markus Kuhn <n04W26...@cl.cam.ac.uk> scribbled the following:
>> (I found it always odd that the Star Trek authors assume,
>> that people will still be saying "metric ton" in the
>> 24th century.)
>
>Have you read many Star Trek books? I have, almost half of all TNG books
>ever written. And I can tell you that not only do they say "metric ton"
>in the 24th century, they routinely still use inches, feet, miles,
>ounces, pounds, etc. This *in conjunction* with metric units. Authors
>switch from one unit system to another at random.

I was refering to the ST:TNG TV series, not to any third-party books.
The TV series was strictly SI. I remember only once or twice having
heard a CGS unit slipped in (erg or dyne), which I guess was by
accident (someone author not having understood the difference
between SI and CGS). There were never any inch/pound units.

Markus Kuhn

unread,

Jun 25, 2004, 4:48:18 PM6/25/04

to

David W. Tamkin writes:
>Do you actually believe the US will ever become fully metric, Markus, or
>are you using that in the sense that once the US has become fully metric,
>donkeys will fly and people will walk on their eyelashes?

I am convinced that US metrication is inevitably going to be
completed within my expected lifetime, that is sometimes in the
next 50 years. I don't think a system of measurement with which now
less than 5% of the world population are familiar has any long-term
survival chances whatsoever in our globally interlinked society.

By "completed", I mean:

- road signs being in km

- more than 50% of the population knowing their height and
weight (if they know it at all) in cm and kg

- no more measurement instruments being produced that display
inch/pound units

- no more business contracts being signed that quote inch/pound units

By these criteria, the UK has not yet completed its metrication
either, but it is very likely to do so in the next 20 years.
Ireland should be there in half this time.

Some inch-based product standards may of course survive for
hundreds of years, until the relevant technology becomes obsolete,
but the fact that some dimensions still found in widely-deployed
specifications are multiples of 25.4 mm will hardly cause
any lot of problems, as todays experience shows.

DWT

unread,

Jun 25, 2004, 5:04:34 PM6/25/04

to

n04W26...@cl.cam.ac.uk (Markus Kuhn) wrote in

<cbi32i$1ah$4...@pegasus.csx.cam.ac.uk>:

| I am convinced that US metrication is inevitably going to be
| completed within my expected lifetime, that is sometimes in the
| next 50 years.

You're optimistic. I think you're unduly optimistic.

Christoph Paeper

unread,

Jun 25, 2004, 6:19:05 PM6/25/04

to

*Markus Kuhn* <n04W26...@cl.cam.ac.uk>:

>
> I was refering to the ST:TNG TV series, not to any third-party books.
> The TV series was strictly SI. I remember only once or twice having
> heard a CGS unit slipped in (erg or dyne), which I guess was by
> accident (someone author not having understood the difference
> between SI and CGS). There were never any inch/pound units.

I remember hearing "megadyne" in TNG and, because I didn't know it, I
thought it was an invented unit just like cochrane(sp?). In another series
(IIRC "Space Rangers" or "Space 2063"/"Space: Above and Beyond") I heard
"klicks" and concluded the same---today I know it's en-US-mil for
kilometre. Both survived the German dubbing. There was something in the
last season of Enterprise, too; pressure measured in ton(ne)s, I believe.

--
The mind is like a parachute; it works much better when it's open.

Dr John Stockton

unread,

Jun 25, 2004, 6:43:29 PM6/25/04

to

JRS: In article <cbgrt1$7t$1...@pegasus.csx.cam.ac.uk>, seen in
news:misc.metric-system, Markus Kuhn <n04W26...@cl.cam.ac.uk> posted
at Fri, 25 Jun 2004 09:39:45 :

>Considering that ISO 31 and ISO 1000 also write "tonne" consistently,
>I have just changed the FAQ to
>
> mass tonne t 1 t = 1000 kg
>
> Note: The tonne (1000 kg) is commonly also called just "ton". The term
> "metric ton" is frequently used in some English-speaking countries for
> 1000 kg, to avoid confusion with other tons still in use there (in
> particular, in the US there is a "short ton" of 907.18474 kg and a
> "long ton" of 1016.046909 kg).

I don't personally find Sec 1.5 greatly helpful on the whole; but I
think that it would be useful to give the exact Imperial equivalents of
the fundamental SI units and of important multiples; or, better, /vice
versa/ (or both).

1 ton = 2240 lb = ... kg
1 pound = 16 ounces = ... kg
1 ounce = ... g

1 mile = ...

That would enable conversion by, or for, Imperial fanatics.

I mean, of course, the Proper Imperial units, such as used in the
British Empire; it would be going altogether too far to include the
diverse units of dissident ex-colonials. Those could be included in a
US Metric FAQ, which Jim could publish in the news:us.* hierarchy.

In the FAQ, "correct spelling" should be "US spelling" or "correct US
spelling".

--
© 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)

Jim Riley

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Jun 26, 2004, 1:31:16 AM6/26/04

to

On Thu, 24 Jun 2004 22:33:48 -0500, Gene Nygaard <gnyg...@nccray.com>
wrote:

>On Fri, 25 Jun 2004 00:35:28 GMT, Jim Riley <jim...@pipeline.com>
>wrote:

>>http://www.usaid.gov/press/releases/2003/pr030321.html

>>
>>Agriculture Secretary Ann M. Veneman and Agency for International
>>Development Administrator Andrew S. Natsios announced the immediate
>>release of 200,000 metric tons of wheat from the Bill Emerson
>>Humanitarian Trust, with another 400,000 tons to be made available as
>>needed.
>
>So what would you conclude--that the first ones are identified because
>they are different from the tons which don't need to be identified in
>the second instance?

I would not make that conclusion.

>>I'm sorry, I do not understand what you are trying to say. Let's
>>start over.
>>
>>The FAQ currently reads (please see FAQ for context):
>>
>> mass ton t 1 t = 1000 kg
>>
>> 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.
>>
>>I suggested that this be changed to:
>>
>> mass tonne t 1 t = 1000 kg
>>
>> Note: The tonne is called the "metric ton" in some English-speaking
>> countries.
>>
>>What specifically are you suggesting?
>
>1 t = 1 Mg

Do you mean to replace the following:
=================================================================

mass ton t 1 t = 1000 kg

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.

=================================================================
With:

=================================================================

1 t = 1 Mg

=================================================================

???

--
Jim Riley

Jim Riley

unread,

Jun 26, 2004, 1:54:32 AM6/26/04

to

On 25 Jun 2004 09:39:45 GMT, n04W26...@cl.cam.ac.uk (Markus Kuhn)
wrote:

>I have just changed the FAQ to

> mass tonne t 1 t = 1000 kg
>
> Note: The tonne (1000 kg) is commonly also called just "ton". The term
> "metric ton" is frequently used in some English-speaking countries for
> 1000 kg, to avoid confusion with other tons still in use there (in
> particular, in the US there is a "short ton" of 907.18474 kg and a
> "long ton" of 1016.046909 kg).

But the term "metric ton" is what the SI Brochure notes as the
alternate spelling in English-speaking countries.

Note: The tonne (1000 kg) is also called the "metric ton",
especially in English-speaking countries. In some case this is
shortened to simply "ton". This may cause confusion in countries
such as the US where a "ton" usually refers to a short ton
907.18474 kg (2000 pounds), or sometimes the long ton
1016.046909 kg (2200 pounds).

--
Jim Riley

Jim Riley

unread,

Jun 26, 2004, 2:05:49 AM6/26/04

to

On Fri, 25 Jun 2004 17:01:28 +0200, Uwe Hercksen
<herc...@mew.uni-erlangen.de> wrote:

>instead of using this sequence: kilotonne, tonne, kilogram, gram,
>milligram, microgram...

The BIPM accepts the use of the tonne in cases where it is the
accepted practice. This recognition is similar to that given the
liter. IIUC, one consideration is whether a switch to use of Mg or
cm^3 might present a health or safety risk. The FAQ is not expressing
a preference for the use of the tonne.

>it would be more consequent to use: gigagram, megagram, kilogram, gram,
>milligram, microgram...

--
Jim Riley

Markus Kuhn

unread,

Jun 27, 2004, 10:26:03 AM6/27/04

to

Dr John Stockton <sp...@merlyn.demon.co.uk> writes:
>I don't personally find Sec 1.5 greatly helpful on the whole; but I
>think that it would be useful to give the exact Imperial equivalents of
>the fundamental SI units and of important multiples; or, better, /vice
>versa/ (or both).
>
> 1 ton = 2240 lb = ... kg
> 1 pound = 16 ounces = ... kg
> 1 ounce = ... g
>
> 1 mile = ...
>
>That would enable conversion by, or for, Imperial fanatics.

No, I deliberately avoided that. Those who look for conversion
factors to/from inch-pound and other units will find excellent
advise in section 3.2 "Where can I look up unit conversion
factors?". Section 3.3 lists those few basic conversion factors
where there exists an exact one by international agreement
(1 in = 25.4 mm, etc.). They are essentially the ones listed
in the appendix of ISO 31.

Why not adding US customary units to section 1.5?

There seems wide agreement among language teachers that it
is far more effective to teach the grammar of a new language
on its own, rather than by relating it in detail to the
grammar of the language the student already knows. Speaking
and understanding a new language should be taught long before practising
to translate between languages. Otherwise, the neural wiring
created for the new language becomes far too dependent on the
old language to ever be able to operate efficiently solely
on its ow.

In the same way, I believe that it is deeply flawed to introduce
people to the metric system by throwing all the conversion factors
for their old system at them. Instead, they should independently
get familiar with interesting quantities solely in the new units.
They will then discover that, at some point, they actually know more
about their world in new units rather than in the old ones, at which
point they will rapidly lose interest in the old units.

People should experience directly what it feels like to drive
100 km/h, rather than to think and know that 80 km/h is
the same as 50 mph.

That is, why a successful metrication effort must at all cost
avoid dual labeling, not only on road signs and product descriptions
but, especially, on measurement instruments. I very much have to
applaud to the approach of the Australian government, which during
their metrication in the late 1970s had for a few years a temporary
law that made it illegal to produce or import measurement
equipment that shows non-metric units. That convinced the
population rather quickly that it is worth the effort to
actually start thinking in the new units.

>In the FAQ, "correct spelling" should be "US spelling" or "correct US
>spelling".

Fair enough.

Esa A E Peuha

unread,

Jun 28, 2004, 5:31:56 AM6/28/04

to

n04W26...@cl.cam.ac.uk (Markus Kuhn) writes:

> I was refering to the ST:TNG TV series, not to any third-party books.
> The TV series was strictly SI.

No it wasn't; it always used lightyears or parsecs to refer to
interstellar distances. SI issues aside, it doesn't make any sense to
use those very Earth-specific units in the ST context, and even more
ridiculously, it doesn't make sense at all to use _both_ units with
approximately equal frequency.

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

Jukka K. Korpela

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Jul 8, 2004, 6:29:11 PM7/8/04

to

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

> AFAIK, 'ton' ist the SI-word for 1000 kg.

No, the standard ISO 1000 says that "tonne" belongs to the set of units
used with the SI, with a footnote saying "Also called the metric ton in
the English language".

The tonne, or the metric ton, is not an SI unit at all. It belongs (along
with the litre) to a set characterized as follows: "There are certain
units, outside the SI, recognized by the CIPM as having to be retained
because of their practical importance".

Using SI units, we would express large masses using the multiples Mg
(which is equivalent to a tonne), Gg, Tg, etc. But it is still uncommon
to do so, and this creates some confusion when people express large
masses in different ways, often using large numbers that could be
dispensed with if we used SI multiples, and often using both kilograms
and tonnes.

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

Keith Harold Elliott

unread,

Jul 10, 2004, 6:55:37 AM7/10/04

to

G'day all readers.
I'm new to all this "Google Group" stuff, but I'm having fun scrolling
through & reading a lot of interesting & crazy comments.
Some people are rich or retired & can spend hours on the net.
I'm poor & busy & I'm lucky if I get an hour per day to do my
computery stuff.
But I've just read some of the "metric" articles & I feel I should
respond. Well, talk about giggle.
We all learned about pounds/shillings/pence, & tons,cwt, furlongs,
fathoms, yards,chains,inches, acres, miles etc when we were kids at
school. Then on Feb 14th 1966, "D" day happened in Australia; decimal
currency was introduced first, then a smoothish changeover to all
things metric over the next year or so. What we ended up with was a
nation of 20 million people who can (mostly) quite comfortably
converse in both "languages". We often hear or read of the suspect who
was described as being 6 feet 2 inches tall & weighing about 90 kilos.
So, blokes & sheilas, what I'm saying to you as a simple Aussie farmer
in desperate need of rain is.......... don't panic, whatever changes
occur, you'll evenually get used to it.

Jukka K. Korpela

unread,

Jul 10, 2004, 6:15:56 PM7/10/04

to

elli...@bigpond.com (Keith Harold Elliott) wrote:

> G'day all readers.
> I'm new to all this "Google Group" stuff,

Welcome. You might benefit from some observations on Usenet, which is
actually what you are using (Google Groups is just an interface):
http://www.cs.tut.fi/~jkorpela/usenet/laws.html

> but I'm having fun scrolling
> through & reading a lot of interesting & crazy comments.
> Some people are rich or retired & can spend hours on the net.
> I'm poor & busy & I'm lucky if I get an hour per day to do my
> computery stuff.

Others who are in a similar position might appreciate brevity - getting
to the point at the start of a message.

And please don't set a followup unless you are really commenting on
someone's message, and in that case quote or explain the main point(s)
you are commenting on.

> What we ended up with was a
> nation of 20 million people who can (mostly) quite comfortably
> converse in both "languages". We often hear or read of the suspect who
> was described as being 6 feet 2 inches tall & weighing about 90 kilos.

Sad to hear that. A random mixture of units is probably much worse than
even the old Anglo-Saxon system. But I still don't see what you are
getting at.

> don't panic, whatever changes
> occur, you'll evenually get used to it.

I wouldn't be so sure. One of the recurring themes in this group is that
we've seen that people (and organizations) do _not_ get used to the
metric system but use a confused mixture of metric and other systems and
also violate the rules of the system when they think they are using the
metric system. And when people finally get somehow used to inevitable
changes, this often takes place through a phase of panic.

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

Dr John Stockton

unread,

Jul 10, 2004, 6:24:47 PM7/10/04

to

JRS: In article <31b1f7b0.04071...@posting.google.com>, seen
in news:misc.metric-system, Keith Harold Elliott <elli...@bigpond.com>
posted at Sat, 10 Jul 2004 03:55:37 :

>G'day all readers.
>I'm new to all this "Google Group" stuff, but I'm having fun scrolling
>through & reading a lot of interesting & crazy comments.

This is an Internet (Usenet) newsgroup; Google have merely vampired on
to newsgroups by providing archiving and a means of access (both, IMHO,
breaches of copyright).

In particular, Google do not control creation deletion or operation of
newsgroups.

Your service provider may run a standard news server; and others are
available, free or cheaply, on the Net. Such are best used with
properly-designed News software, available on similar terms for most
computers. Those can provide better facilities than a Web interface
does.

Of course, if for example you access the Net through a Public Library
system, you may have no choice.

--
© John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 MIME ©
Web <URL:http://www.uwasa.fi/~ts/http/tsfaq.html> -> Timo Salmi: Usenet Q&A.
Web <URL:http://www.merlyn.demon.co.uk/news-use.htm> : about usage of News.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

Chris Savage

unread,

Jul 12, 2004, 7:37:56 AM7/12/04

to

On 2004-07-10, Jukka K. Korpela <jkor...@cs.tut.fi> wrote:
> elli...@bigpond.com (Keith Harold Elliott) wrote:
>
>> G'day all readers.
>> I'm new to all this "Google Group" stuff,
>

> And please don't set a followup unless you are really commenting on
> someone's message, and in that case quote or explain the main point(s)
> you are commenting on.
>

But he didn't set a followup. I'm not even sure that's possible from
Google.

--
Chris Savage Kiss me. Or would you rather live in a
Crawcrook,UK land where the soap won't lather?

gra_f...@yahoo.com

unread,

Jul 13, 2004, 9:25:55 PM7/13/04

to

On 10 Jul 2004 03:55:37 -0700, elli...@bigpond.com (Keith Harold
Elliott) wrote:

>G'day all readers.
>I'm new to all this "Google Group" stuff, but I'm having fun scrolling
>through & reading a lot of interesting & crazy comments.
>Some people are rich or retired & can spend hours on the net.
>I'm poor & busy & I'm lucky if I get an hour per day to do my
>computery stuff.
>But I've just read some of the "metric" articles & I feel I should
>respond. Well, talk about giggle.
>We all learned about pounds/shillings/pence, & tons,cwt, furlongs,
>fathoms, yards,chains,inches, acres, miles etc when we were kids at
>school. Then on Feb 14th 1966, "D" day happened in Australia; decimal
>currency was introduced first, then a smoothish changeover to all
>things metric over the next year or so.

Australia went metric in the early 70's, during the Whitlam years. I
remember it well. I started school the year we adopted decimal
currency and I can still remember the jingle. I learnt, feet, yards,
miles etc until hight school, then we learnt metric.

> What we ended up with was a
>nation of 20 million people who can (mostly) quite comfortably
>converse in both "languages".

My brother is 8 years younger than me, in his mid 30's. He's got no
idea about imperial measurements. He might say "an inch" in
conversation but that's it.

> We often hear or read of the suspect who
>was described as being 6 feet 2 inches tall & weighing about 90 kilos.

You do?

Esa A E Peuha

unread,

Jul 14, 2004, 4:31:32 AM7/14/04

to

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

> And please don't set a followup unless you are really commenting on
> someone's message, and in that case quote or explain the main point(s)
> you are commenting on.

You mean "don't follow up on someones message unless...", right? That's
different from setting a Followup-to: header field.

Markus Kuhn

unread,

Jul 15, 2004, 2:42:05 AM7/15/04

to

Archive-name: metric-system-faq
Posting-Frequency: monthly
Last-modified: $Date: 2004/07/15 06:41:27 $
Version: $Revision: 1.44 $
URL: http://www.cl.cam.ac.uk/~mgk25/metric-system-faq.txt

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
standards. If "Ω" does not show up as a Greek capital letter omega,
chances are that chosing a different font with a larger Unicode
repertoire to read this text may help.

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 mathematics 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, claimed that
teaching solely metric measurements could save an estimated 82
days of mathematics 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 can 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 (in air): 340 m/s

Speed of light (in air or vacuum): 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 speed of passenger planes: 600-800 km/h

Cruise altitude of passenger planes: 10 km

Official altitude boundary between Earth's
atmosphere and space ("Karman line"): 100 km

E) Temperatures

Lowest possible temperature: -273.15 °C = 0 K

Typical freezer temperature: -18 °C

Freezing water/melting ice: 0 °C

Drink with many ice cubes: 0 °C

Temperature of highest density of water: 4 °C

Typical refrigerator 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 (at sea level): 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 (US) spelling, abbreviation and typesetting of SI
unit names: