Today is extra auspicious since it is the once-in-a-century Rounded Up Pi Day, when the month, day and year are pi correct to four decimal places rounded up to the nearest decimal place, the Guardian reports.

Pi is 3.14159 to five decimal places. Rounded up to four it is 3.1416. And today is 3/14/16.

Pi is the ratio of the circumference to the diameter of a circle, and it is a very useful number in maths. For example, to calculate the area of a circle you multiply pi by the square of the radius (that’s the distance from the centre to the side), which is summarized by the formula “Circle area = πr2.” This may be useful information.