Pi is the ratio of a circle’s circumference to its diameter. Pi (*) has a decimal value of 3.14. In 1706, British mathematician William Jones devised the * symbol to represent the ratio, and it was later popularized by the Swiss mathematician Leonhard Euler.

Pi Approximation Day is celebrated on 22 July and Pi Day is celebrated on 14 March. Casual Pi Day is also known as Pi Approximation Day.

**Pi Approximation Day: History**

Nearly 4000 years have passed since Pi was first discovered. Circular dimensions were calculated using this value – approximated to 3.125 – by ancient Babylonians. Around 250 B.C. Archimedes of Syracuse, one of the greatest ancient mathematicians, calculated pi for the first time. He found that pi fell somewhere between 3 1/7 and 3 10/71. Pi is occasionally referred to as the ‘Archimedes’ Constant.’

Another brilliant mathematician, Zu Chongzhi, computed pi again in the mid-400s. Zu calculated pi himself in a novel way since Archimedes’ books were lost. It was Zu and Archimedes who was the first to understand pi in any true sense.

Later on, mathematicians tried to approximate pi better using circumscribed and inscribed polygons. For 1,000 years, Archimedes used this method to calculate pi for the first time. In 1630, Austrian astronomer Christoph Grienberger reached 38 correct digits of pi using this method.

In the 16th- and 17th centuries, the infinite series (the sum of terms of an infinite sequence) revolutionized how pi is calculated. While Indian mathematicians discovered it between 1400 and 1500 A.D., it was European mathematicians like Leibniz and Gregory who popularized it a century later. The Greek symbol pi was first used to represent pi in 1706, despite pi being a well-known concept for centuries. William Jones, a Welsh mathematician, proposed this in 1737, but Leonhard Euler popularized it.

Read More: 22 July in Indian and World History

Modern computing power is dedicated to approximating the infinite, irrational number to the fullest extent. The first-time pi was calculated by a machine was in 1957, when George Reitwiesner and John von Neumann used an ENIAC computer. There were many intrepid mathematicians who followed. This method reached a million digits by 1973.

**Pi Approximation Day** **depends upon the format of the Date**

According to timeanddate.com, the day depends on the format of the date. On 22 July or 22/7, some countries where dates are written in the date/month format celebrate Pi Approximation Day or Casual Pi Day. Meanwhile, those who write their dates in month/date format celebrate Pi Day on 14 March (3/14 or 3-14). Due to the fact that the first three digits of the date corresponding to the first three digits of pi (3.14).

**Facts about pi**

- pi is irrational that is not equal to the ratio of any two whole numbers. Its digits do not repeat and for everyday calculations, an approximation like 3.14 or 22/7 is often used.
- The value of pi to 39 decimal places is 3.141592653589793238462643383279502884197.
- It’s indicated by the Rhind papyrus that ancient Egyptians used a value of 256/81 or about 3.16045.