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.
--------------------------------------------------------- Tom Wade | EMail: tee dot wade at eurokom dot ie EuroKom | Tel: +353 (1) 296-9696 A2, Nutgrove Office Park | Fax: +353 (1) 296-9697 Rathfarnham | Disclaimer: This is not a disclaimer Dublin 14 | Tip: "Friends don't let friends do Unix !" Ireland
