On Mar 11 , at 4:48 PM, John Frewen-Lord wrote:
There I suggest using cm (sorry Pat N), as people can then express
their height verbally as, say, One Seventy Eight - which can be
interpreted by the listener as either 178 cm or 1.78 m - both are
the same value.
John says you can say "one seventy-eight" and in can easily be
understood to mean 1.78 m or 178 cm. However, you can also say "one,
seven-eighty" which can be easily interpreted as 1.780 m or 1780 mm
(which are also the same value). That argument fails in showing that
centimetres are better than millimetres for this measurement.
It really is NOT easier one way or the other. Some things seem easier
just because we're more familiar with them.
Virtually all other prefixes in SI are multiples of 1000. The
centimetre is the ONLY commonly used SI unit that uses the prefix
"centi". (Emphasis on "common".) As such, it is reasonable to suggest
that we drop it so we have one less prefix to bother with.
Yes, I know that the centimetre is still an official part of SI, but
if it is unnecessary, we don't have to use it. SI tells us what we MAY
use in SI; it does not tell us that we MUST use an particular part of
it.
It seems funny to me, too, to report my height in millimetres. I first
learned my height in metric on a centimetre measuring rod. So I
learned 181 cm and I became familiar with that. I often find it
convenient to refer to it my height as 1.81 m but I know some people
are uncomfortable using fraction ("Why", I'll never know!) and,
therefore, they feel more comfortable with 181 cm. But there really is
nothing wrong, difficult or awkward about using 1810 mm.
I would agree that it would probably need to be understood that such
measurements are good only to the nearest 10 mm, that is, the trailing
zero is usually not a significant figure. However, there are plenty of
example in daily life where we use numbers that large and we might
have problems understanding the implied precision, and they seem to
give us no trouble. Some examples (in our comfortable Olde English
units) are:
The distance from New York to San Francisco is about 3000 miles.
Last year I earned $75,000. (I didn't, by the way!)
The Dow John Average has fallen over 7000 points since it's
highest value.
Mt. Everest is 29,000 feet high.
I paid $113,000 for that house.
The distance to the moon is 239,000 miles.
I use about 1500 gallons of gas a year in my car.
The NFL season rushing record is over 2000 yards.
I have only about 17000 frequent flyer miles.
The speed of sound is a little over 1000 ft/s.
If we're not turned off by these and hundreds of other example with
numbers over 1000, then why are we bothered by my height stated as
1819 mm?
(That previous sentence is NOT merely a rhetorical question; we ARE
bothered and I'm asking if you know why. Do you know?)
Bill Hooper
1810 mm tall
Fernandina Beach, Florida, USA
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SImplification Begins With SI.
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