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.
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Tom Wade | EMail: tee dot wade at eurokom dot ie
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