A simple sector, for use with dividers to do mathematical calculations involving proportions. Also called the proportional compass, or military compass.

Print in two pieces, friction should be enough to hold them together. The hinge should be tight enough that it holds its position, but not so tight that it won't open and close.

I printed mine in white, then ran a marker across the raised scales.

To use it, you also need a compass (like for drawing circles), or simple dividers: https://www.thingiverse.com/thing:6793282