If you've seen a couple of my recent Facebook posts, you know that I went on a quest for a compass -- not the "where's north" type of compass, but the "draw a circle" type of compass. The reason I wanted one is to make drawing concentric circles easier. Compasses are very good for that. You could even say that circle drawing the raison d'etre of the compass. Concentric circles make a very nice framework for fancypants Zentangle-ish mandala drawing.
I found my compass at Target, part of a "math kit" consisting of a ruler, protractor, two triangles, pencil and sharpener, graphite tips, eraser, and two -- count 'em, two! -- compasses. One compass uses a graphite tip; the other the traditional pencil.
The pencil compass immediately brought back memories of 10th grade and Geometry class with Sister Anne Cecelia. Sister Anne Cecelia was an elder nun with poor eyesight. She was a great Geometry teacher. She could draw a perfect freehand circle on the blackboard. Before tests and quizzes, she would intone, "Time will pass; will you?"
Anyway, because of her poor eyesight, she required all of us to do our homework in jet black ink. Pencil was not allowed. If Sister Anne couldn't see your work, you effectively didn't do it. So how in the world could we draw the jet black circles necessary to prove all those theorems without screwing it up?
Imagine our excitement when Flair felt-tip pens appeared! They were God's gift to Sister Anne's Geometry students.