In the UK 3, 6, 12, 24, 36......etc. are round numbers. Elsewhere it is 5, 10, 20....100 and beyond. One example of a superbly simple and natural concept of measurement is the chain, a unit of length equal to 66 feet (22 yards). It is subdivided into 100 links or 4 rods. There are 10 chains in a furlong, and 80 chains in one statute mile. Bring it back and cherish it, .....and advance ?