Stumbled across this today. It may be old, but it’s the first that I have seen it.
Great illustration of the basic concept.
I like it 
I remember that one, when I was in the army I was tasked by my 1st Sargeant to tutor a class of students basic electronic I made a drawing of a “moat” that made a square. The anology seemed to work they all passed.
Ah yes Army … :-k . Saw some of their cartoon manuals. 