After you make it all the way around, the program calculates the circumference and radius of your circle—and from that, the value of pi. You can see the code by clicking the pencil icon.

This is at least my ninth year of writing about Pi Day— here is my post from 2010. Of course it's called Pi Day because the date, 3/14, is similar to the first three digits of pi (3.1415 …).