Pi Approximation Day is observed on March 14, because of the Ancient Greek mathematician Archimedes' first rough approximation of π as being 3.14. (A few years later, Archimedes was able to calculate a much better approximation of π.) However, this date may be considered misleading, because 22/7 is actually a closer approximation of π than 3.14 is. Thus, a "correct" Pi Day could be found in the European calendar, 22/7, or July 22.
And it is Pearlie's Day as well - no approximation about that :)