On Wednesday 03 December 2008 21:41:04 Pat Naughtin wrote: > 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.
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. The milligram per deciliter can be stated without using a prefix in the denominator as the centigram per liter or decagram per cubic meter. Pierre
