Pencil

A dot generator also capable of making lines, although not the coke version.

Pencils are characterized as being sharp an pointy on one end, and flat on the other. Sometimes a rubber (or eraser) is attached to the flat end, allowing one to make as many mistakes as one wished, safe in the knowledge that one can rub them out. Unfortunately the eraser is an example of an area eraser. Therefore it always erases a collection of dots instead of a single dot, unless the dots are far enough apart to escape the erasing effect of the area eraser. You can calculate this distance by measuring the width of the eraser. If the dots are further apart than the width of the area eraser then with skill, it is possible to erase a single dot in a collection of dots with the area eraser.