The secret of the wheels Change the diameter and compare C/d. The contour changes, but the ratio in the model remains π. Explore the controls and explain what changed in your own words. Ative o JavaScript para ver esta figura interativa. Archimedes’ constant, known as pi (Π) was widely studied in Greece (around the 3rd century BC). It all started with the study of one of the most important figures in geometry, which is the circle. This constant is obtained by the ratio ($\div$) of the length of the circumference and the diameter.