This probably the figure first taught in elementary school, Pi (3.14159).
I never knew where the figure is derived from since my teacher also dint knew it.
So, do you know that Pi is the length of a circle with 1cm diameter?
Assuming we have a wheel with 1cm diameter and we take the length of that wheel using a rope, tied in to the wheel, then the length of rope needed is 3.14159 meters. The comparison value on the circular length and the diameter of the circle is always constant for each circular at 3.14159. Also, Pi can be interpreted as 1 full circular of a circle or in other words, 1Pi = 360 degree.