A Rival Constant

March 14 only spells 3.14 in the American date order; in much of the world (14/3) the joke falls flat. Some mathematicians push a rival: Tau Day on June 28, since tau = 2 x pi is about 6.283.

Their case is real, not just pedantic. Tau equals one full turn, so a circle is tau radians, not 2pi. Formulas that use 2pi everywhere get simpler. But pi has thousands of years of habit behind it, and habit is hard to beat.