Pi or pie, whether you’re a baker or a math whiz, today is your day — Pi Approximation Day on July 22 honors the concept of pi, which is denoted by the Greek letter pi and approximates to 3.14, in the most mathematically-pleasing way. To further make punny jokes out of pi day, many bake pies on the holiday. It’s a great day to appreciate the math concept used so regularly in many calculations, and eat some delicious pie!

**History**

Pi has been known for nearly 4000 years in some form or another. Ancient Babylonians used it — approximated to 3.125, to calculate the dimensions of circles. It was around 250 B.C. that pi was first calculated by one of the greatest ancient mathematicians, Archimedes of Syracuse. He found that pi fell somewhere between 3 1/7 and 3 10/71. Pi is occasionally referred to as the ‘Archimedes’ Constant.’

Later, in the mid-400s, another brilliant mathematician, Zu Chongzhi, computed pi again with lengthy calculations. Since Archimedes’ books were lost, and not in China at that time, Zu calculated pi himself in a novel way. Between Zu and Archimedes, these two scientists were the first to know pi in any true sense.

Later, mathematicians attempted to better approximate pi using circumscribed and inscribed polygons. This was how Archimedes first solved for pi, and it remained the dominant algorithm for pi computation for 1,000 years. The most correct approximation achieved using this method came in 1630, with Austrian astronomer Christoph Grienberger, who arrived at 38 correct digits of pi.

With the development of the infinite series (the sum of the terms of an infinite sequence) in the 16th- and 17th centuries, the way pi was calculated was revolutionized. In India, they discovered it early, between 1400 and 1500 A.D., yet it’s European mathematicians like Leibniz and Gregory who popularized it a century later. Though pi was a well-known concept for centuries, it wasn’t until 1706 that the Greek symbol pi came to represent it. This was suggested by William Jones, a Welsh mathematician, but not popularized until it was used by Leonhard Euler in 1737.

In modern times, endless amounts of computing power have been dedicated to approximating the infinite, irrational number to the fullest extent possible. The first time pi was computed by a machine was in 1957, when George Reitwiesner and John von Neumann used an ENIAC computer to compute 2,037 digits of pi. Many intrepid mathematicians followed. By 1973, a million digits were reached with this method.

The calculation of pi became a useful stress test for a computer’s abilities — almost like a test for the heart. Mathematicians also hoped to have more accurate calculations for pi for cosmology, though, for most pursuits, few digits are needed. Emma Haruka Iwao, a Google employee who calculated more digits of pi than anyone else to this point — 31 trillion, has earned a place in the Guinness Book of World Records.

Credit: National Today