It is once again Pi Day (March 14—which is like the first digits of pi: 3 and 14). Before getting into this year's celebration of pi, let me just summarize some of the most important things about this awesome number. Outside the US, Pi Day should probably be July 22 (22/7)—this fraction is a surprisingly good estimate of pi. You can find the value of pi with a mass and a spring. The value of pi is related to the local gravitational field.