williamsheil, I agree with you insofar as it is wrong to try and impose a standard world unit on anyone. Perhaps my 'proof' leans rather to much in the direction of 'I'm gonna tell you the real truth' and in retrospect I would change some of the wording. When you are shuffling pieces of a puzzle around, and suddenly they all seem to fall into place, there is a great temptation to shout 'Eureka'. Perhaps the 'proof' should be looked upon more as a technical curiosity? As I said in my first post, I am not suggesting anyone adopt 8.602, in fact just the opposite. In my reply to Grey cat above, I quote an example where a world unit which defies convention suits a particular purpose very nicely. Ian