Google marked Pi Day – the date made up of the first three digits of the mathematical constant pi – with a doodle on Wednesday. The Greek letter π (pi) represents the ratio between a circle’s circumference and its diameter, which is the same for every circle. When expressed up to two decimal places, this ratio is 3.14 – same as March 14 written in digits.

Wednesday marks the 30th anniversary of the first time Pi Day was recognised in 1988 by physicist Larry Shaw.

Pi is one of the most commonly known mathematical constants. The ratio between the circumference – the length of a thread held along the periphery of a circle – and the diameter – the maximum distance between two points on a circle – is an irrational number, which means it has infinite decimal places. Approximate values used most commonly in calculations are 3.14 and 3.1415, or the fraction 22/7.

The doodle was made by pastry chef Dominique Ansel, Google said. In a video, Ansel described making a caramel apple pie, which he said is a very “scientific and precise” process. He also gave a recipe of the apple pie. Eating pies is one of the ways mathematics enthusiasts celebrate Pi Day.