On 2008/12/18, at 1:47 AM, Tom Wade wrote:
I meant the latter rule. Stated precisely: Do not use units that
are a power of 10 times a coherent SI unit, but are not a power of
1000 times a coherent SI unit. That cuts out the are, hectare, and
tog, as well as the centimeter and the deciliter.
As Pat Naughtin explained in USMA:42129, this is not an official
'Rule of 1000' at all, but a practice seen in some industries.
The use of the phrase 'Rull of 1000' to refer to the above is
misleading. There is an official 'Rule of 1000' in the NIST web
page, and it refers to the use of the appropriate prefix to produce
a number between 1 & 1000. It specifically states that it allows
"*centimeters* [my emphasis] or millimeters to be used where a
length declaration is less than 100 centimeters."
Thus the NIST rule far from deprecating cm actually recommends
them. To use the phrase "Rule of 1000" to refer to the attempted
exclusion of perfectly valid prefixes such as centi & deci lends far
more official credence than it merits.
Dear Tom,
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.
As an example, here is a description of the processes we used for the
metric transition in Australia. The original article is from a state
government web page for the state of Victoria where I live, you will
find it at: http://www.consumer.vic.gov.au/CA256EB5000644CE/page/Trade+Measurement-Educational+Material+and+Links-Metrication+-+information+for+students?OpenDocument&1=930-Trade+Measurement
~&2=930-Educational+Material+and+Links~&3=0-Metrication+-+informat
##
UNITS RECOMMENDED FOR USE
The Board and its committee had given particular attention to the
metric units which should be recommended both for general use and for
specific purposes. The policy of the Board was to retain the benefits
of the inherent simplicity of the SI units to the greatest possible
extent, while recognising that some additional units would be required
for convenience in trade, technology and everyday use. A non-SI unit
or a special name for a unit would be recommended where there was a
clear need for such a unit by powers of 1000. Thus for measurements of
volumes of liquids the litre (1) would be the commonly used unit with
its decimal sub-multiple the millilitre (10³ 1) for smaller volumes.
No need was seen for the use of the centilitre (10² 1) or the
decilitre (10¹ 1).
By avoiding the unnecessary proliferation of special unit names it was
believed that the range of units needed for everyday use would only
involve combinations of about 10 unit names with five prefixes. More
than half of these 15 words were already in common use.
In most sectors of activity there were types of measurement, which
were of particular concern to the sector. Thus the builder would be
concerned with the measurements of length, area and volume, the
surveyor with length, area and angle and the pharmacist with mass and
volume. As appropriate each Sector Committee was being asked to select
from the units available those recommended for general or particular
use in that sector. Thus the building and construction industry had
recommended their length measurements be made and expressed only in
millimetres and metres (not centimetres) whereas the clothing industry
favoured the use of metre and centimetre. It was proposed to publish
documents giving guidance on the usage proposed in regard to units for
sectors of activity as appropriate. In important cases these could be
formalised as Australian Standards, for example the Australian
Standard AS 1155-1971 "Metric Units in Construction" listed selection
of preferred units for the construction industry.
##
The result of this policy as it was applied was that the building
industry had completed its metric transition mostly within a year and
at most two years with their their length measurements (be) made and
expressed only in millimetres and metres (not centimetres) while the
clothing industry is still struggling with a mish-mash of centimetres,
inches, yards, feet, and metres, with halves, quarters, eighths, and
tenths of all of these, after 38 years (so far) having favoured the
use of metre and centimetre.
Changing the subject slightly, I have to say that I don't really know
why it is that centimetres are so unsuccessful, although I do have
some thoughts on the subject. I have yet to find an example where a
metric transition went smoothly, quickly, and economically using
centimetres. Probably, the most dramatic example in English speaking
nations is the issue of human height in centimetres; even after about
40 years in Australia, Canada, New Zealand, South Africa, and the UK
the metrication of human height has barely begun.
Cheers,
Pat Naughtin
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that they
now save thousands each year when buying, processing, or selling for
their businesses. Pat provides services and resources for many
different trades, crafts, and professions for commercial, industrial
and government metrication leaders in Asia, Europe, and in the USA.
Pat's clients include the Australian Government, Google, NASA, NIST,
and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com
for more metrication information, contact Pat at [email protected]
or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter
to subscribe.
