On Jan 22, 12:57, Max Eskin wrote: The whole system is based on units that are matched to each other in such a way that the constants involved in relating units to other units work out to unity. So the kilogram just happens to be a handier quantity than a gram, and saves a lot of dividing or multiplying by 1000. Except, of course, in real life, where units are rarely handy sizes at all :-) On Jan 22, 13:28, Cameron Kaiser wrote: is 1,000 cc It was originally intended to be a cubic decimetre of water at it's maximum density. Unfortunatley, that turned out to be 28 ppm to large -- the constants I mentioned above don't quite work out to unity. So it was changed to an arbitrary amount to suit -- and the litre was defined as the volume of water that had that mass at it's maximum density. Hence a litre was actually 1000.028 cm^3. Since that just moves the "obviously silly" constant to a different place in the scheme, it was redefined later to be exactly 1000 cm^3, but with the recommendation that it not be used for work of high accuracy. Hmmm.... and we thought IBM were having trouble with the megamaths. -- Pete Peter Turnbull Dept. of Computer Science University of York