Pat Naugthin wrote in USMA 21372:
>Please don't misunderstand me. I'm not suggesting that any official SI units
>(e.g. millilitres and millimetres) are technically inferior or superior to
>any other units (e.g. centilitres and centimetres). What I am saying - as
>strongly as I can - is that for any nation that is currently in the process
>of metrication, the choice of millimetres and millilitres will hasten the
>process remarkably.
>
>I used to say that you could teach a builder's laborer enough SI units to
>construct a house in 50 minutes - using millimetres; and it takes at least
>50 years to teach a clothing worker enough SI units to construct a skirt -
>using centimetres, and I only had my tongue slightly in my cheek.
> If you choose
>centimetres as the small unit of length for metrication at your place of
>work, you should also settle down for the 50 year wait for the conversion
>process to be complete.
>Pat Naughtin CAMS
South African Metrication News, 1978-07/08 wrote:
1. One of the most important aims of the SI is the simplification and
rationaliation of units, both for measurment and for use in calculations.
The number of multiples and sub-multiples is accordingly restricted by
giving preference to the use of prefixes that represent steps of 1 000 (x
10^3)
2. If this preferred range of prefixes is combined with the division of
numerals into groups of three then this makes for extreme ease of
converssion from, say mm to m by simply moving the decimal indicator to the
next aoolicable space viz:
1 725 352 mm = 1 725,352 m = 1,725 352 km
3. If the centimetre is interposed between the millimetre and the metre
it has several disadvantages:
(i) It destroys the simplicity of the system,
(ii) It makes it impossible to use the *groups of three* method to
change from centimetres, say, as the gap is in the wrong place viz:
76 322 cm = 763,22 m
But there will be a tendency - using the *gap* theory - to make the answer
76,322 m (a tenfold error).
(iii) It is universal practice in technical drawings to use
millimetres only. If this practice is employed all that has to be done is
to write *all dimensions in millimetres* at the top of the drawing and then
leave all symbols off each dimension - a tremendous saving of time and
ensuring that errors in transcription are avoided.
If centimetres are permitted as well as millimetres then it would be
necessary to use symbols again after every dimension and the risk of error
in transcription is very great indeed.
4. It should be noted that the objection to centimetre is confined to
its use as a linear measure. When raised to the second and third powers, as
in areas and volumes respectively, it is necessary to employ square
centimetres and cubic centimetres to render the steps betweeen successive
multiples of area and volume, practical ones.
5. In South Africa the centimetre is used in the clothing and textile
industries and therefore also for related dimensions of the the human body.
It should, preferably, not be introduced elsewhere.
6. If the centimetre were given equal status with the millimetre we
would have the situation where some people would specify the dimensions of,
say, a piece of paper in centimetres and others would specify its
dimensions in millimetres. This would be very confusing and would defeat
one of the main objects of introducing a univeersal language of
measurement.
7. There is no doubt that the preference that many people have for the
centimetre is merely aother throw-back to the imperial system - it is the
sub-multiple of the metre that is most closely relatred to the inch - and
such people naturally tend to use it in all applications where the inch was
previojsly used. This "cross-section" of people is, however a dimnishing
one.
9. The SI, if it is to retain its simplicity and its coherency, must
employ as few sub-multiples and multiples as possible. Nobody wishes to
interpose centigram between milligram and gram, for example, nor
centinewton between millinewton and newton, nor centivolt between millivolt
and volt, etc., and basically there is no reason why the measurement of
length should require special treatment when it has been proven to be
unnecessary for mass, force, electrical potential, etc.
Joseph B.Reid
17 Glebe Road West
Toronto M5P 1C8 Tel. 416 486-6071
