getting info off dying hard drive

[Amanda Ripanykhazova]

Got a HDD which started dying while downloading 10.7.4 update. Whole
computer froze completely

Now will only boot to recovery partition and then perform all checks
properly! But reinstalling OS involved going online, confirming
everything and then starting the Lion download which doesnt download
(like as the update didn't download?) If you wait, it will oblige by
telling you that the transfer will take 111 hours, which is apple's
way of saying that the file isnt downloading.

DU from the recovery partition reports no problems on the drive and
curiously DW can run to completion on the node check AND write a
replacement directory and report successful completion!!

But thereafter, nothing can get the computer to work with this hard
drive in it. (It DOES work fine with another HDD so isn't the
computer). It will now boot only to the recovery partition, i cant
even do an R start to diagnose the hardware.

Would anyone have any idea why the computer can access the drive, DW
can write a whole directory structure to completion whereas nothing
can transfer an update or OS file to the drive itself? Is it likely
that anything is recoverable on this drive before I dump it please?

[Jolly Roger]

In article
<72409cd4-f8ed-4427...@j25g2000yqn.googlegroups.com>,

If it were really important data that was not backed up (an extreme
rarity for me, personally), I'd try a disk recovery solution on it. Have
a look at this review:

<http://mac-hard-drive-recovery-review.toptenreviews.com/>

--
Send responses to the relevant news group rather than email to me.
E-mail sent to this address may be devoured by my very hungry SPAM
filter. Due to Google's refusal to prevent spammers from posting
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Groups. Use a real news client if you want me to see your posts.

JR

[nospam]

In article
<72409cd4-f8ed-4427...@j25g2000yqn.googlegroups.com>,
Amanda Ripanykhazova <license...@gmail.com> wrote:

> Got a HDD which started dying while downloading 10.7.4 update. Whole
> computer froze completely
>
> Now will only boot to recovery partition and then perform all checks
> properly! But reinstalling OS involved going online, confirming
> everything and then starting the Lion download which doesnt download
> (like as the update didn't download?) If you wait, it will oblige by
> telling you that the transfer will take 111 hours, which is apple's
> way of saying that the file isnt downloading.
>
> DU from the recovery partition reports no problems on the drive and
> curiously DW can run to completion on the node check AND write a
> replacement directory and report successful completion!!

if disk warrior can run to completion, use its preview mode and copy
everything off. start with the most important stuff.

if you want to clone it, try carbon copy cloner, which will skip files
it can't copy and tell you which ones afterwards. superduper will abort
the clone on any error which is dumb.

> But thereafter, nothing can get the computer to work with this hard
> drive in it. (It DOES work fine with another HDD so isn't the
> computer). It will now boot only to the recovery partition, i cant
> even do an R start to diagnose the hardware.
>
> Would anyone have any idea why the computer can access the drive, DW
> can write a whole directory structure to completion whereas nothing
> can transfer an update or OS file to the drive itself? Is it likely
> that anything is recoverable on this drive before I dump it please?

likely bad blocks affecting critical files.

[Amanda Ripanykhazova]

On May 24, 8:01 am, nospam <nos...@nospam.invalid> wrote:
> In article
> <72409cd4-f8ed-4427-afb2-8e3ebf489...@j25g2000yqn.googlegroups.com>,

Thanks for that, I didnt realise that you could copy onto another
drive in DW: I have the drive in a freezer now for a while and will
put it back in the MacBook and try to get the data back onto a USB
drive. I wonder if I can put a blank new drive into the computer,
boot off the DVD, scan the bad drive (if i can figure out how to work
the infernally complex SATA to USB connector I bought in HongKong),
and "clone" everything onto the new drive?

Yes, i suspected bad blocks but posted here because both DU and DW
seem to be telling me that there arent any bad blocks: Unless SMART
has already replaced the bad blocks with spare ones and the drive
LOOKS ok now: In which case, I wonder why the Lion Install Process
cant transfer anything TO the drive? Hopefully this shouldnt prevent
DW copying OFF the drive!

[nospam]

In article
<6568a7c0-8620-4669...@r3g2000yqh.googlegroups.com>,

Amanda Ripanykhazova <license...@gmail.com> wrote:

> Thanks for that, I didnt realise that you could copy onto another
> drive in DW: I have the drive in a freezer now for a while and will
> put it back in the MacBook and try to get the data back onto a USB
> drive.

ugh. it's a bit late now, but that's not a good idea. put the drive
inside a baggie as it warms up.

> I wonder if I can put a blank new drive into the computer,
> boot off the DVD, scan the bad drive (if i can figure out how to work
> the infernally complex SATA to USB connector I bought in HongKong),
> and "clone" everything onto the new drive?

clone it with carbon copy cloner which will skip files it can't read.

> Yes, i suspected bad blocks but posted here because both DU and DW
> seem to be telling me that there arent any bad blocks: Unless SMART
> has already replaced the bad blocks with spare ones and the drive
> LOOKS ok now: In which case, I wonder why the Lion Install Process
> cant transfer anything TO the drive? Hopefully this shouldnt prevent
> DW copying OFF the drive!

smart just tells you it's within spec or not, not that it's about to
fail. if smart finds something out of spec then there's a good chance
the drive will fail, but if it doesn't, that doesn't mean nothing is
wrong. it could be fine, or it could be about to fail (but still within
spec).

[Amanda Ripanykhazova]

On May 24, 10:53 am, real-address-in-...@flur.bltigibbet.invalid
(Rowland McDonnell) wrote:
> Amanda Ripanykhazova <licensedtoqu...@gmail.com> wrote:
>
> [snip]

>
> > Thanks for that, I didnt realise that you could copy onto another
> > drive in DW: I  have the drive in a freezer now for a while and will
> > put it back in the MacBook and try to get the data back onto a USB
> > drive.
>

> I've read plenty of reports on the Web of that method helping in some
> cases, but if I were you, I'd let the thing warm up to room temperature
> again before starting it up.  It sounds like your HDD is currently
> working okay, just with some data damage which is preventing normal
> operation of the OS - and a sub-zero HDD is at risk from damaging itself
> if you start it up.
>
> Best to try DW or Carbon Copy Cloner to get the data off before trying a
> last-ditch desperate method.
>
> This bloke suggests warming up for 24 hours at room temperature as a
> sensible precaution - it's what I'd do too:
>
> <http://www.pcguide.com/care/care/gen/env_Ambient.htm>
>
> In addition to what he mentions, HDDs have lubricants in them: they work
> best at operational temperature.  Too cold, and the lubricants will be
> more viscous than the mechanism expects, which means the lubrication
> won't be working as expected.
>
> In extreme cases, this can prevent a HDD starting up or cause damage.
>
> Just done some Web searching: seems that a typical minimum environment
> temperature for operating a HDD is 5 degrees celsius.

>
> >  I wonder if I can put a blank new drive into the computer,
> > boot off the DVD, scan the bad drive (if i can figure out how to work
> > the infernally complex SATA to USB connector I bought in HongKong),
> > and "clone" everything onto the new drive?
>

> It'd be worth trying.  Might be best to buy a proper external HDD
> enclosure.
>
> Rowland.
>
> --
> Remove the animal for email address: rowland.mcdonn...@dog.physics.org
>                                             Sorry - the spam got to mehttp://www.mag-uk.org                           http://www.bmf.co.uk
> UK biker?   Join MAG and the BMF and stop the Eurocrats banning biking

Thanks for that guys, I have been using the freezer method for some
years now but always wondered when exactly to try the drive again. I
could never quite reconcile whether I needed to use the drive while
all interior parts were in a contracted state and therefore could move
easier if they were jammed; or whether the contraction itself let
the parts which weren't (for example) moving move freely again (for a
while).

[Amanda Ripanykhazova]

On May 25, 8:38 am, real-address-in-...@flur.bltigibbet.invalid
(Rowland McDonnell) wrote:
> nospam <nos...@nospam.invalid> wrote:

> > Amanda Ripanykhazova <licensedtoqu...@gmail.com> wrote:
>
> > > Thanks for that, I didnt realise that you could copy onto another
> > > drive in DW: I  have the drive in a freezer now for a while and will
> > > put it back in the MacBook and try to get the data back onto a USB
> > > drive.
>
> > ugh. it's a bit late now, but that's not a good idea. put the drive
> > inside a baggie as it warms up.
>

> The HDD needs to be sealed up in a bag for the chilling down so as to
> avoid picking up extra moisture which will condense.
>
> If the HDD has not been sealed up in a bag inside the freezer, the best
> idea (I think) is to wrap it up for warming up over (say) 12 hours, and
> then unwrap it and leave it for another 24 hours exposed at room
> temperature for the extra moisture it's picked up inside the freezer to
> evaporate.
>
> Put it somewhere the cat can't get at it...
>
> Rowland.


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Here's the results: The freezing may have worked. I let it warm up
for a few hours and then was able (again) to DW the drive.

I then transferred the data across to another drive (Make sure it is
formatted HFS or DW won't see it, which is a bit annoying)

I then started up and it went into recovery mode so I wasted some time
trying to reinstall the OS. This time the transfer worked to some
degree!! The reinstall started transferring the OS to the computer
[excruciatingly slowly: There may be a problem with DW's network
settings?]. But at about 90% of the transfer the problems cropped up
again and the drive stopped being able to write the data it was
transferring.It stopped with a message that the transfer had 1 hr
54mins left. The next day the message hadnt changed.

It would be nice to get the drive working, do a backup, get a new
drive and hurl this one into the garbage (or contact Hitachi and get
them to replace it!! It says it was made in May 2010!) but now
everything should be OK and all I need is to figure out how to
reinstall Lion onto a blank drive. Whether there is an easier way than
to install SL and then upgrade to Lion.

Still, at least I was able to get the 20 gig VM off the drive before
it died which makes reinstalling Windows 7 on the new one a breeze
instead of a real pain in the neck!

> Remove the animal for email address: rowland.mcdonn...@dog.physics.org
>                                             Sorry - the spam got to mehttp://www.mag-uk.org                           http://www.bmf.co.uk
> UK biker?   Join MAG and the BMF and stop the Eurocrats banning biking

Here's the results: Th

[isw]

In article
<1kknk94.1k00obl1qo7xhcN%real-addr...@flur.bltigibbet.invalid>,
real-addr...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:

--snip--

> The point of the freezer method is to use the HDD when in a chilled down
> state - but it's a risky thing to be doing, and not one to try until all
> other methods have been exhausted.

That trick has always bothered me. All hard drives are vented (through
air filters) to equalize pressure, inside and out. If all the interior
surfaces are very cold, why wouldn't atmospheric water vapor enter and
condense all over everything? (Which, I assume, wouldn't do the drive a
whole lot of good).

If chilling really did anything good, it seems to me that it'd be better
to leave the driv in the freezer while trying to get the data off it.

Isaac

[Walter Bushell]

In article
<1kklvcz.1gfe9miw9xks0N%real-addr...@flur.bltigibbet.invalid>,
real-addr...@flur.bltigibbet.invalid (Rowland McDonnell)
wrote:

> Just done some Web searching: seems that a typical minimum environment
> temperature for operating a HDD is 5 degrees celsius.

Ah, so in Fahrenheit the answer would be 42!?

--
This space unintentionally left blank.

[Walter Bushell]

In article
<1kkpeny.k2fyzwckh728N%real-addr...@flur.bltigibbet.invalid>,
real-addr...@flur.bltigibbet.invalid (Rowland McDonnell)
wrote:

> Walter Bushell <pr...@panix.com> wrote:
>
> > (Rowland McDonnell) wrote:
> >
> > > Just done some Web searching: seems that a typical minimum environment
> > > temperature for operating a HDD is 5 degrees celsius.
> >
> > Ah, so in Fahrenheit the answer would be 42!?
>

> Alas, 41. Shame - thought you might have hit upon the ultimate question
> to life, the universe and everything: `What is the minimum operating
> temperature for a hard disc drive'.
>
> Rowland.

Ah, give me a degree for a safety factor?

[Dr Eberhard W Lisse]

When these things happen to me (very rarely) I restore from time machine.

I synchronize my machines with Unison to my desktops at home and the
practice, which both have external drives connected, and the AirBook I
connect to the travel hard disk before and after I travel :-)-O

Since my sons get the hand-me-downs after I upgrade they are used to
restoring from their time machines to the new(er) boxes :-)-O

el

On 2012-05-25 14:27 , Amanda Ripanykhazova wrote:
[...]

> Here's the results: The freezing may have worked. I let it warm up
> for a few hours and then was able (again) to DW the drive.
>
> I then transferred the data across to another drive (Make sure it is
> formatted HFS or DW won't see it, which is a bit annoying)
>
> I then started up and it went into recovery mode so I wasted some time
> trying to reinstall the OS. This time the transfer worked to some
> degree!! The reinstall started transferring the OS to the computer
> [excruciatingly slowly: There may be a problem with DW's network
> settings?]. But at about 90% of the transfer the problems cropped up
> again and the drive stopped being able to write the data it was
> transferring.It stopped with a message that the transfer had 1 hr
> 54mins left. The next day the message hadnt changed.
>
> It would be nice to get the drive working, do a backup, get a new
> drive and hurl this one into the garbage (or contact Hitachi and get
> them to replace it!! It says it was made in May 2010!) but now
> everything should be OK and all I need is to figure out how to
> reinstall Lion onto a blank drive. Whether there is an easier way than
> to install SL and then upgrade to Lion.
>
> Still, at least I was able to get the 20 gig VM off the drive before
> it died which makes reinstalling Windows 7 on the new one a breeze
> instead of a real pain in the neck!

[...]

--
If you want to email me, replace nospam with el

[David Stone]

In article
<1kkpeia.hhl8to1jeuej0N%real-addr...@flur.bltigibbet.invalid>,
real-addr...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:

> isw <i...@witzend.com> wrote:
>
> > real-addr...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:
> >
> > --snip--
> >
> > > The point of the freezer method is to use the HDD when in a chilled down
> > > state - but it's a risky thing to be doing, and not one to try until all
> > > other methods have been exhausted.
> >
> > That trick has always bothered me. All hard drives are vented (through
> > air filters) to equalize pressure, inside and out. If all the interior
> > surfaces are very cold, why wouldn't atmospheric water vapor enter and
> > condense all over everything?
>

> Atmospheric water vapour is already inside the thing, to an extent.
> What extent? I dunno - but all the Web advice on freezing HDDs I've
> read includes the instruction to wrap the HDD up in a plastic bag to
> avoid condensation.

The issue is not so much atmospheric water vapour in the drive when
you put it IN the freezer (unless you live somewhere like Hong Kong),
but atmospheric water vapour condensing on the cold surfaces when you
bring it OUT, until it warms up to room temperature.

[Amanda Ripanykhazova]

On May 28, 8:51 am, David Stone <no.em...@domain.invalid> wrote:
> In article
> <1kkpeia.hhl8to1jeuej0N%real-address-in-...@flur.bltigibbet.invalid>,

>  real-address-in-...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:
>
>
>
>
>
>
>
>
>
> > isw <i...@witzend.com> wrote:
>

> > >  real-address-in-...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:
>
> > > --snip--
>
> > > > The point of the freezer method is to use the HDD when in a chilled down
> > > > state - but it's a risky thing to be doing, and not one to try until all
> > > > other methods have been exhausted.
>
> > > That trick has always bothered me. All hard drives are vented (through
> > > air filters) to equalize pressure, inside and out. If all the interior
> > > surfaces are very cold, why wouldn't atmospheric water vapor enter and
> > > condense all over everything?
>
> > Atmospheric water vapour is already inside the thing, to an extent.
> > What extent?  I dunno - but all the Web advice on freezing HDDs I've
> > read includes the instruction to wrap the HDD up in a plastic bag to
> > avoid condensation.
>
> The issue is not so much atmospheric water vapour in the drive when
> you put it IN the freezer (unless you live somewhere like Hong Kong),
> but atmospheric water vapour condensing on the cold surfaces when you
> bring it OUT, until it warms up to room temperature.

If it is true (and I have never found that it is) I am shocked to hear
that these drives aren't sealed! Doesnt the manufacturer take all
sorts of egregious steps to completely seal even the room where they
are made to obviate the whole dust and moisture situation? Is it
suddenly being suggested that once the drives hit the road, the seals
are no longer important such that moisture can get in?

[Amanda Ripanykhazova]

On May 28, 8:51 am, David Stone <no.em...@domain.invalid> wrote:
> In article
> <1kkpeia.hhl8to1jeuej0N%real-address-in-...@flur.bltigibbet.invalid>,

>  real-address-in-...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:
>
>
>
>
>
>
>
>
>
> > isw <i...@witzend.com> wrote:
>

> > >  real-address-in-...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:
>
> > > --snip--
>
> > > > The point of the freezer method is to use the HDD when in a chilled down
> > > > state - but it's a risky thing to be doing, and not one to try until all
> > > > other methods have been exhausted.
>
> > > That trick has always bothered me. All hard drives are vented (through
> > > air filters) to equalize pressure, inside and out. If all the interior
> > > surfaces are very cold, why wouldn't atmospheric water vapor enter and
> > > condense all over everything?
>
> > Atmospheric water vapour is already inside the thing, to an extent.
> > What extent?  I dunno - but all the Web advice on freezing HDDs I've
> > read includes the instruction to wrap the HDD up in a plastic bag to
> > avoid condensation.
>
> The issue is not so much atmospheric water vapour in the drive when
> you put it IN the freezer (unless you live somewhere like Hong Kong),
> but atmospheric water vapour condensing on the cold surfaces when you
> bring it OUT, until it warms up to room temperature.

By the way, I am wondering about testing these devices with numerous
connected at the same time, - whether I can (without a Time Machine
backup of the drive) connect numerous drives at the same time and
backup QUICKLY before the drive dies/freezes again. Does anyone have
any idea how these drives can be connected to the firewire port on the
Macbook or should I start a new thread on this? The GoFlex suggests
(actually a myserious thing called a Limited Edition) that it comes
with a simple cable which connects SATA to USB as well as another one
which connects the SATA port on the drive to the FireWire 800 port on
the MBP! Is it really this easy and can I just connect any SATA drive
with a simple cable to the Firewire port on the computer?

[isw]

In article
<f2fd97b9-6fe4-4175...@j25g2000yqn.googlegroups.com>,
Amanda Ripanykhazova <license...@gmail.com> wrote:

-- snippage --

> By the way, I am wondering about testing these devices with numerous
> connected at the same time, - whether I can (without a Time Machine
> backup of the drive) connect numerous drives at the same time and
> backup QUICKLY before the drive dies/freezes again.

No matter how many destination drives you have, all the data necessarily
has to come from the source drive. Trying to get several files off it
simultaneously will result in lots of interleaved seek operations, which
might not be a good thing. I doubt there's anything faster than a
straight cloning operation. For speed, Firewire *might* be faster, but
it could depend on implementation or how many other things your computer
was doing at the same time.

> Does anyone have
> any idea how these drives can be connected to the firewire port on the
> Macbook or should I start a new thread on this? The GoFlex suggests
> (actually a myserious thing called a Limited Edition) that it comes
> with a simple cable which connects SATA to USB as well as another one
> which connects the SATA port on the drive to the FireWire 800 port on
> the MBP! Is it really this easy and can I just connect any SATA drive
> with a simple cable to the Firewire port on the computer?

It's not exactly a "simple cable"; it has a pretty sophisticated chip
(or chips) inside to handle the conversion, but yes, that's really all
it takes. For 2.5" drives, often the power to run them can be supplied
via USB, but 3.5" drives usually need an external power supply.

One advantage of an external case (maybe the only one) is that you don't
have to futz around with the power supply issue if you feel
uncomfortable messing with things like that.

IME, inexpensive adapters work about as well as expensive ones. I've had
my external DVD burner running through a $4.00 SATA-to-USB adapter I got
off eBay for a couple of years with no problems at all. My Time Machine
disk is also USB-connected.

Isaac

[isw]

In article
<1kkte1x.1r3djcu5uhk5kN%real-addr...@flur.bltigibbet.invalid>,
real-addr...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:

> Amanda Ripanykhazova <license...@gmail.com> wrote:
>
> > David Stone <no.em...@domain.invalid> wrote:
> [snip]

>
> > > The issue is not so much atmospheric water vapour in the drive when
> > > you put it IN the freezer (unless you live somewhere like Hong Kong),
> > > but atmospheric water vapour condensing on the cold surfaces when you
> > > bring it OUT, until it warms up to room temperature.
> >
> > If it is true (and I have never found that it is) I am shocked to hear
> > that these drives aren't sealed! Doesnt the manufacturer take all
> > sorts of egregious steps to completely seal even the room where they
> > are made to obviate the whole dust and moisture situation?
>

> The manufacturing environment for hard disc drives is air-conditioned
> and so on to prevent dust getting in, and I expect that humidity is
> controlled too. But the moisture content will surely be greater than
> zero whatever they do; then again, I don't know exactly how they make
> HDDs these days, and for all I know they're made inside automated
> micro-environments where the atmospheric moisture content can be made as
> near to zero as makes no odds.
>
> As for being sealed up: the thing is that a hard disc drive is a box
> containing air. The box needs to avoid being warped out of shape,
> because that's a Bad Thing from the point of view of operation of the
> disc drive.
>
> If the box were fully sealed up, changes in ambient pressure would
> result in air pressure forces on the box, which would distort it - just
> think about travelling by aeroplane, for example, or just driving to
> Mexico City.
>
> The solution is to have a very small air-pressure balancing hole - from
> what I've read about it, it's not just a hole in the case, but a long
> wiggly and very narrow duct designed to prevent the ingress of dust: the
> idea (so I've read) is that any dust which does get in to the duct ends
> up stuck to the wall.

That is exactly correct. One side of the serpentine channel is formed
by the bottom side of the adhesive label on the case, so the sticky goo
grabs any particles that come past. Then at the inside end, there's a
small but very effective air filter to handle anything that gets all the
way through.

There's also a similar filter positioned so that air moving around
because of the spinning disk will pass through it. This takes care of
particles that get loose inside after the disk is in service.

Isaac

[Walter Bushell]

In article
<1kkpj2y.1joeoff1yi4r27N%real-addr...@flur.bltigibbet.invalid>,

real-addr...@flur.bltigibbet.invalid (Rowland McDonnell)
wrote:

> Walter Bushell <pr...@panix.com> wrote:
>
> > (Rowland McDonnell) wrote:
> >
> > > Walter Bushell <pr...@panix.com> wrote:
> > >
> > > > (Rowland McDonnell) wrote:
> > > >
> > > > > Just done some Web searching: seems that a typical minimum environment
> > > > > temperature for operating a HDD is 5 degrees celsius.
> > > >
> > > > Ah, so in Fahrenheit the answer would be 42!?
> > >
> > > Alas, 41. Shame - thought you might have hit upon the ultimate question
> > > to life, the universe and everything: `What is the minimum operating
> > > temperature for a hard disc drive'.
> > >
> > > Rowland.
> >
> > Ah, give me a degree for a safety factor?
>

> For those of us living in the developed world[1], it's more like 5/9ths
> of a degree (celsius).
>
> Rowland.
>
> [1] ;-) But seriously, when *is* the USA going to go metric? Like
> (almost) every other nation on Earth[2]?
>
> <http://en.wikipedia.org/wiki/Metric_system#Usage_around_the_world>
>
> [2] Look, the UK uses metric for trade, science, and industry - and has
> fudged it so as to keep some things like miles on road signs and pints
> for milk and beer, because people are attached to 'em.
>
> - except those apparently `imperial' units are all defined using
> metric. You get most of the benefits of metric while appeasing a lot of
> the objectors. Surely something like the bodged job we've got in the UK
> would suit the USA?

The US measures are also defined in terms of metric. One inch is 2.54
centimeters by definition and hence we gain all the improvements of
precision from the metric world.

[Simo...@canada.com]

In article
<1kkz0nc.1rvobnasb2akoN%real-addr...@flur.bltigibbet.invalid>,

real-addr...@flur.bltigibbet.invalid (Rowland McDonnell) wrote:

> Walter Bushell <pr...@panix.com> wrote:
>
> > (Rowland McDonnell) wrote:

> [snip]

>
> > > [2] Look, the UK uses metric for trade, science, and industry - and has
> > > fudged it so as to keep some things like miles on road signs and pints
> > > for milk and beer, because people are attached to 'em.
> > >
> > > - except those apparently `imperial' units are all defined using
> > > metric. You get most of the benefits of metric while appeasing a lot of
> > > the objectors. Surely something like the bodged job we've got in the UK
> > > would suit the USA?
> >
> > The US measures are also defined in terms of metric.
>

> Indeed, but metric units are commonly not actually directly used.

>
> > One inch is 2.54
> > centimeters by definition and hence we gain all the improvements of
> > precision from the metric world.
>

> The improvement in precision comes purely from improvements in
> metrology, not the system of units.

I would not agree with this statement, under certain conditions. For
instance, Fahrenheit has more degrees (180) between freezing and boiling
than metric does. Like Metric has more cm per inch. So when, in common
conversation, you say it is 40 degrees in Fahrenheit, you are more
accurate than if you say it is 4 degrees C. Because 40F = 4.44C. So 4C
is about half a degree off, and is actually very near 39F. (And in
common conversation, seldom does anyone go to one digit past the zero,
as it usually gets into a region that our bodies are not capable of
interpreting, anyway.

Likewise, if you say something is 15cm, that is more accurate than if
you way it is 6", because 6" really equals about 1/4 cm over 15 cm.

if you are working in a scientific environment, then you are right,
because if you go to three digits past the decimal point, the
differences become a factor of improvements in metrology, as you
correctly state. OIt is only in conversation that a measure with more
units is more accurate.

>
> For example, the only fundamental unit that's still defined in terms of
> a physical object is mass[1].
>
> The accuracy and precision of the methods used to get from `unit
> definition' to `practical application of that definition' have improved
> hugely since the metric system was first introduced - but purely due to
> advances in the science and technology of measurement, not the units in
> use.
>
> Metric's great advantage is a gain in *consistency* of units, leading to
> easier international communication in trade, science, engineering, and
> even politics (when considering exactly where a border might be, for
> example). This means all international dealings depending on
> measurement work faster with much less scope for confusion, to the
> benefit of all.
>
> The consistency advantage applies to non-metric units defined in terms
> of the global measurement standards - but if many nations do not use the
> non-metric units, their use negates the communication advantages of
> metric[2]. Moreover, using odd units can lead to confusion even inside
> nations which do use non-metric units (see below).
>
> Once upon a time, there were lots of different yards and inches[3] and
> pounds and miles (as in `different number of feet per mile') and so on -
> one of the main benefits of a set of international standards of
> measurement is that everyone's working to the same standards, which is
> good for trade and science[4] and engineering.
>
> - except that in the USA, two different sets of linear measurement are
> currently in use: the modern version (which defines 1 inch as 25.4mm),
> and the old "survey mile", version: defined as 1 foot = 1200/3937 m and
> 1 mile = 5280 feet.
>
> <http://en.wikipedia.org/wiki/Foot_%28unit%29#Survey_foot>
> <http://en.wikipedia.org/wiki/Mile#Statute_mile>
>
> Continuing to use a mix of units - some "English" and some metric - does
> lead to confusion and problems from time to time.
>
> E.g:
> <http://en.wikipedia.org/wiki/Mars_Climate_Orbiter#Cause_of_failure>
>
> NASA stopped permitting suppliers to work in anything other than metric
> after that cockup (except in exceptional circumstances, apparently -
> I've not found out what that might cover).
>
> Rowland.
>
> [1] And they're working on a better replacement definition - with the
> embarrassing impetus of unexplained excessive variations between the
> various international standard kilograms.
>
> <http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_international_pr
> ototype_kilogram>
>
> [2] It came out recently that the EU's strong attempts in the 1980s to
> get the UK to ban the use of all Imperial units was because the gnomes
> of Brussels (Martin Bangemann in particular) wanted to remove what they
> perceived as the UK's trading advantage with the USA caused by the fact
> that we understand your units. Possibly they missed the point US fluid
> measures are different from ours and have always confused the hell out
> of me.

The US gallon is actually 80% of an Imperial gallon. An ounce is an
ounce but a quart in US is smaller than imperial - there are almost 5 US
quarts in an imperial gallon. Clearest definition for me is that 1 Gal
Imperial = 4.54 liters; one US Gallon = 3.8 liters.

>
> [3] The old French inch was significantly larger than the English inch
> of the day, which caused Napoleon Bonaparte to often be described as
> short despite being of average height for men of his time.
>
> <http://en.wikipedia.org/wiki/Napoleon#Image>
>
> [4] When using scientific results from pre-SI days, it's very important
> to make sure you know exactly what measurement standards were being used
> if you want proper precision and accuracy. And even in the SI era, the
> temperature scale has been fiddled about with: IPTS 68 and ITS 90
> measurements give different apparent temperatures for the same real
> temperature.

S.