I don't know how many out there are aware of the controversy about pi being the "right" choice for the circle mathematical constant. If you don't know about it yet, the nice video below by Vi Hart will update you with some fun. Here is some more thorough stuff - as far as it goes, anyway. It's called "the Tau manifesto", Tau being, well, two times pi. And, unlike this, the Tau thing is meant to be for real.