This discussion ignores the basic fact that all professional groups
establish, sooner or later, a standards practice manual. That is the
document that guides the use of units and prefixes, among other items. As an
example, drafting in any engineering (mechanical, electric, nuclear,
chemical, bio-mechanical, .............) has settled on mm
(implied!) for dimensioning, and the member bodies of course are bound to
follow. Individuals or even some small company may not be aware of the
existence of their professional society (they all charge annual fees) and
that ignorance will always exist in free societies.
To inform professionals about the use of mm vs. cm is a matter of directing
them to their society's guidebook. I doubt that any such manual anywhere in
the world would not stipulate mm for dimensioning. If it did, it would be in
a section "exemptions" and supported by reasoning. We might address that
exemption if we are savvy enough in that profession to develop an argument.
Stan Jakuba
PS: It helps to keep in mind that dimension and distance mean different
things.
----- Original Message -----
From: "Robert H. Bushnell" <[email protected]>
To: "U.S. Metric Association" <[email protected]>
Cc: <[email protected]>
Sent: 09 Jan 05, Monday 12:34
Subject: [USMA:42252] Re: Rule of 1000
Tom,
You argue too much. You want science to do public policy. I want
simple examples. I say use millimeter. Example: Say I build an
intersection of roads. I lay out the curbs in millimeters, 30 000 mm
apart.
Then I place the posts to hold the traffic lights, again in millimeters,
say 2 000 mm from the curb. Next I put down the bolts to hold the posts,
400 mm apart. All the post hardware is in millimeters. But say some
drawing shows the road in meters and centimeters, possibly 6 276.34 m or
627634 cm with the bolt centers spaced in millimeters. Having both
centimeters and millimeters on a drawing is risky. They are too close
in size. A unit size ratio of 1000 makes errors unlikely.
But Tom, thanks for your attention to these matters.
Robert Bushnell PhD PE
On Jan 5, 2009, at 8:42 AM, Tom Wade wrote:
A very Happy New Year to you Pat, and all the other contributers in this
group.
I agree with you that the prefix centi is a legitimate parts of the SI
as are deci deca and hecto. However, as I have stated here before, the
use of centi during a metric transition delays the successful
introduction of the metric system dramatically.
With respect, you have not demonstrated this. You have established a
correlation between industries that chose cm and slow metrication. This
is not necessarily a causal link in that had they chosen mm instead the
change would have gone faster.
For example, McDonalds once claimed that it was extremely rare for
countries that had established chains of its restaurants to ever go to
war with each other (the claim may well have been tongue-in- cheek). The
fact that such a correlation did exist does not prove that eating
McDonalds hamburgers makes you less warlike. The two facts (reduced
chance of warfare & McDonalds restaurants) both have a common
influencing factor: in this case the presence of relatively affluent
free market economies, which makes warfare as opposed to trade
unattractive.
The equivalent for the cm vs mm is that some industries (e.g. building,
engineering) require a high degree of precision in measurement. For
such industries moving from fractions of an inch to whole mm yields a
large advantage, and is thus an incentive to fast metrication. Such
industries perform many calulations based on such measurements, and ease
of manipulation of metric quantities is far superior to its imperial
counterparts.
Industries like clothing, or anything requiring measurement of people's
height does not need millimeter precision. Indeed it would simply not
work. A waist size of 80 cm will suit people of 793 mm to 848 mm,
without the need to produce a tenfold increase in the range of pants
size. Similarly measuring people's height in mm would be absurd, as it
would vary wildly depending on posture and haircut.
Of course, going from an older system which used half-inch as the
smallest increment to whole centimeters is a plus, but not anything like
the advantage in going from 3 3/8 inches to mm equivalent, so the win
factor of metrication is not as apparent. On the other hand personal
body measurements are the ones that produce the most resistance to
change, as people have typically compared them to older generations, and
you have to overcome the familiarity factor. Also such measurements are
used purely for comparison, and not to do any arithmetic manipulation on
them.
Thus an industry sector that chooses cm rather than mm will be prone to
a slower migration. This is not to say the choice of cm caused it, but
that the factors that led to cm being the right choice will act as a
brake on metrication. The crucial difference between the above and what
you asserted is what is predicted if the industry instead chose mm. If
the above is correct, choosing to migrate clothing or human height
measurement to mm would lead to even more resistance to change since the
numbers would be more awkward, or clothing sizes would be too diverse.
If the original assertion were correct, choosing mm would result in a
faster migration.
What we need to do apply the scientific method. Both hypotheses predict
that industries choosing cm will be slower to migrate, so it is useless
to compare different industries. What we need to do is find an example
of such an industry elsewhere that did choose mm, and compare the ease
of its migration to its equivalent that chose cm.
It is important to establish which is correct, as otherwise we won't
find the right way to provide the best incentivization to such
industries to complete the change to metric - which is what we all want.
---------------------------------------------------------
Tom Wade | EMail: tee dot wade at eurokom dot ie
EuroKom | Tel: +353 (1) 296-9696
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