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... Representing the ratio of a circle's circumference to its diameter, pi is approximately equal to 3.14159 -- but its digits go on forever. In school, you might have used it to calculate the area of a circle or the volume of a cylinder. But the applications of pi are endless and part of every corner of our world.

The holiday was created in 1988 by Larry Shaw, a physicist at the Exploratorium science museum in San Francisco.

"He had a very open and expansive view of the world and saw an opportunity with this number, mathematical concept, to invite people into the joy of mathematical learning," said Sam Sharkland, program director of public programs at the museum, who worked with Shaw before he died in 2017.

While it began as a small staff celebration featuring pie, it soon turned into a grand procession where hundreds of visitors marched around the pi shrine, each carrying a digit. Attendees often show up early to claim their favorite digit for the parade. One woman who has the symbol tattooed on her neck comes every year and marches near the front with a pi flag, Sharkland said.

The celebration begins at 1:59 p.m., signifying the next three digits of pi. ...