SAN FRANCISCO (KGO) -- Pi symbolizes the ratio of a circle's circumference to its diameter, or 3.14, as in today's date.
RELATED: Using pie to explain Pi in honor of Pi Day
Pi Day started at San Francisco's Exploratorium and it's the 30th anniversary. To celebrate, there will be tons of free events starting at 10 a.m.
Click here for a list of event for Pi Day at the Exploratorium.
Free Pi Day events taking place at the Exploratorium in San Francisco
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