How San Francisco made Pi Day a cultural holiday

• Shaw came up with the idea over three decades ago after pondering his fascination with pi, the mathematical constant that is a ratio of a circle's circumference to its diameter.

How it happened: The first Pi Day was March 14, 1988. At 1:59 — the numbers immediately following 3.14 in the pi sequence — Shaw and his wife set up a table with fruit pies and a tea urn at the museum.

• Shaw also installed a circular brass plaque at the center of a circular classroom made from circular cinder blocks — it was deemed the "Pi Shrine."

What they did: Annual festivities have included a parade around the museum led by Shaw, who would blare the digits of pi to the music of "Pomp and Circumstance Marches" on a boombox.

• The parade ended after circumnavigating the Pi Shrine 3.14 times while singing "Happy Birthday" to Albert Einstein. He has been honored with a celebration of his life every year after Shaw's daughter discovered that March 14 was also Einstein's birthday.

The big picture: The homegrown tradition eventually expanded and led Congress to recognize Pi Day in March 2009.

• The UN similarly declared March 14 the International Day of Mathematics in 2019.

What's inside: This year, pi-related activities at the Exploratorium include the Pi Parade, which will feature local brass and percussion band Mission Delirium, free pie slices and demonstrations showcasing pi's uses in science and art.

• Visitors can also learn the mathematically optimal way to slice a pie, according to the museum.
• For those unable to make it in person, the Exploratorium has created a guide for celebrating on your own.