Sorry my next comment has nothing to do with your post from English Phrasal Verbs (27/365) - It happens Accross.
It's just that when I saw the image the first thing that came to my mind was a class of mathematics with the number Pi, the teacher used that image to explain us. It is an irrational number and one of the most important mathematical constants.

That image I associate with that concept. Sorry to leave the subject.