Of course, arithmetic to the base 12 -which is what the £sd system (and the foot/inch system) was- is more logical, from the mathematical point of view than the decimal system. 12 has the six factors 1,2,3,4,6,12 whereas 10 only has the four factors 1,2,5,10. This means that there are more short-cuts available. The UK should have stayed with £sd and the rest of the world should have given up on decimal. But computers came along and forced the change. Shame. Roger Lovegrove Please do visit the LOVEGROVE Information Centre on http://www.lovegrove.f9.co.uk/ons/