Garry, thanks for the explaination.Sidetraking further, we in the UK must have been responsble for some of the most illogical systems going - why 12 inches make a foot, 3 feet a yard... is it 1760 yards in a mile? Then there are chains, furlongs etc. somewhere in the middle... And then there are weights, volumes etc. Which leads me to another one - why is a US gallon smaller than a UK one?
Jon