Thursday is National Pi Day

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LANSING, Mich. (WILX) - Thursday is the 14th day of the third month. If you break that down, it's 3, 1, and 4. Those digits are crucial, because they make March 14 National Pi Day.

It's not pie as in apple pie or pizza pie, but pi as in the mathematical constant 3.14 represented by the Greek letter Pi.

It's the ratio of a circle's circumference to its diameter.

It's been celebrated since 1988.