People really don't appreciate the compass enough. This is a pretty intricate version, below, but even the simple ones have this incredible cross-functionality with unknown drawing devices, and are built to be capable of use with a variety of writing instruments that the compass-maker cannot possibly know the dimensions and attributes of. It's also one of the simplest solutions to drawing a perfect circle, and we forget how many others came and went in the face of this wicked beast of a device. God, I love them.