The Babylonians used 3.125 for Pi. This value was found "by calculating the perimeter of a hexagon inscribed within a circle and assuming that the ratio of the hexagon’s perimeter to the circle’s circumference was 24/25." (The Editors of Encyclopaedia Britannica 2019)

The Babylonian's introduce place value with their sexagesimal (base-60) number system (historyworld.net). However, their system involved "ambiguous spacing" which made it difficult to interpret (Berlinghoff 2015).

The Rhind Papyrus tells us that the Egyptians approximated Pi to be 3.1605.

The first usage of Roman Numerals began showing up between 900 and 800 BC (Hom 2013).

A Greek philosopher of the Pythagorean brotherhood. He is responsible for discovering irrational numbers (also referred to as "incommensurable numbers"). People disagree on Pythagoras' reaction to learning about irrational numbers, but one theory is that he was so upset he threw Hippasus off a boat to sea. (The Gale Group Inc. 2001)

Archimedes was the first person to use calculations to approximate Pi. He found upper and lower bounds for the area of a circle using polygons inscribed and circumscribed within a circle. He found the value of Pi to be between 3 10/71 and 3 1/7 (exploratorium.edu).

Ptolemy used 377/120 for Pi.

Zu Chongzhi approximated Pi to be 355/113 using a method adopted from Liu Hui (265 A.D.). He held a record for 800 years for having seven digits of accuracy (Ye 2016).

Indian mathematician Aryabhata used (62832/20000) for pi

The "hour" officially refers to 1/24 of a day (Oxford Reference).

Leonardo da Vinci painted "The Last Supper"

William Oughtred of England published "Clavis Mathematice" which emphasized "the importance of using mathematical symbols." Oughtred used the symbols +, -, and = as we use them today. (Berlinghoff 2015)

Blaise Pascal created a machine comprised of geared wheels that could add and subtract two numbers directly and also multiply and divide them by repetition. (McFadden 2018)

William Jones used the greek letter π to name Pi. Leonard Euler adopted it in his publications in the 18th century.

Johann Lambert, a German mathematician, proved π is an irrational number.

William Shanks spent more than 15 years computing a decimal value for Pi by hand to 607 places. The first 527 digits are correct.

ENIAC (first electronic computer) calculated 2,037 digits of pi in 70 hours (scientificamerican.com)

Curt Herzstark is responsible for the only handheld pocket calculator ever created. Herzstark was sent to Buchenwald Concentration Camp during WWII because of his Jewish father, but he was saved due to his intelligence. The Nazi's treated him as an "intelligence-slave." (McFadden 2018)

Emma Haruka Iwao calculated Pi to 31.4 trillion decimal places. Her and her team used the ycruncher program powered by 25 virtual machines run through Google Cloud's Compute Engine (Molina 2019).

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