Why do we use a number system based on 10? 10 can only be divided evenly into halves; 12 on the other hand can be divided into halves, quarters, and thirds. The strangest thing of all is that in the U.S. we use a measuring system based on 12 but a numbering system based on 10! How irrational! Changing to a 12 based numbering system would be relatively simple and would make counting and dividing much easier - too bad everyone's too "set in their ways." Between this and the 12 month calendar, I don't know which is a bigger travesty to human rationality.