On 2008/11/29, at 10:12 AM, James Frysinger wrote:
Pierre,
Please tell me where in the SI Brochure the "rule of 1000" can be
found. I don't seem to see it in my copy.
Jim
Dear Jim,
The 'rule of 1000' appears on the NIST web page at http://ts.nist.gov/WeightsAndMeasures/Metric/metric.cfm
when you search for 'rule of 1000'. It reads:
Rule of 1000 -- The selected multiple or submultiple prefixes for SI
units shall result in numerical values between 1 and 1000. This rule
allows centimeters or millimeters to be used where a length
declaration is less than 100 centimeters. For example: 500 g not 0.5
kg; 1.96 kg not 1960 g; or 750 mL, not 0.75 L, or 750 mm or 75 cm, not
0.75 m;
Interestingly, this differs from the advice given in the International
Standards Organization booklet, 'ISO SI Guide: International System of
Units', where they write:
Prefixes are used to avoid large or small numerical values, but note
that the multiples and sub-multiples are not coherent SI units. The
prefix should generally be chosen so that the numerical value will be
between 0,1 and 1 000, but, this is not always possible or even
desirable.
The ISO document does not, however, refer to this as a 'Rule of 1000'.
After an example, they go on to say:
In certain cases the same prefix should be kept irrespective of the
numerical value. For example in tables and diagrams the same unit
should be used for all quantity values and on technical drawings only
millimetres should be used.
I have never seen a decent formulation of the 'rule of 1000' and I
don't believe that the 'Rule of 1000' ever really had much direct
relevance during any metrication transition except insofar as it
tended to favor choices of whole numbers rather than mixed numbers,
decimals, or vulgar or common fractions. I have met another 'rule of
1000' in practice most often as the engineering principle where they
choose to use only those SI prefixes from the 20 available that are
multiples of 1000, leaving them with only 16 prefixes after they
denigrate the use of centi, deci, deca, and hecto.
Lately, I am moving more toward the idea of a 'Whole number rule'
where prefixes are chosen for a particular activity in such a way as
to provide whole numbers for most activities in a particular field.
Such a policy could, I think, be formulated relatively simply for each
activity. As a reminder here is the policy that was successfully used
in the Australian building industry:
The metric units for linear measurement in building and construction
will be the metre (m) and the millimetre (mm), with the kilometre (km)
being used where required. This will apply to all sectors of the
industry, and the centimetre (cm) shall not be used. (Standards
Association of Australia 'Metric Handbook, Metric Conversion in
Building and Construction 1972)
This policy choice had the effect that all measurements on all
building jobs have been done in whole numbers since 1972. There has
been no need for mixed numbers, decimal fractions, or common or vulgar
fractions since then. The immediate net result was that the metric
transition in these trades was smooth, rapid, and complete.
I have argued in the past that this success was due to the choice of
millimetres rather than centimetres but, while that is still true, I
now think that the underlying choice that made whole numbers prevalent
has also played a major role in the smoothness of these metrication
upgrades.
As you know, I have elaborated on these themes at:
http://www.metricationmatters.com/docs/WholeNumberRule.pdf
And at: http://www.metricationmatters.com/docs/centimetresORmillimetres.pdf
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]
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