I heard someone mention in passing there is a reason everything through antiquity to now has used base 12 instead of base 10.  Time is kept in twelve hour/twenty four hour incriments, 12 months in the year...why?  And while the metric system is base 10 and is used worldwide, it is certainly not the favored unit of measurement in the USA.  Any ideas?    

Each of the little numbers has a lot of tradition. Please consider that even when some units are 12-based, they still are embedded within the 10 (0-9)- based number system, even in Anglo-American-tradition countries. The Romans had a (non-)system which must have been a pain for every bookmaker. Some authors I've read claim that the 10-based number system is not accidental, but holds a deeper truth. Mathematically it doesnt matter in which system we encode the quantity of elements of a set. But the cardinal numbers of course have different mathematical properties, such as being a prime number and such. A mathematician might tell you the specifics of the cardinal number 12.

Spooky