This is a simple speed square.  It is a tool commonly used by construction tradespeople to quickly mark 90°, 45°, 22.5°. and 10° angles.  

It also includes a 140mm ruler along the bottom edge.

Numbers are more visible if filament color is changed after layer 2 and layer 18 when printing with 0.2mm layer heights (0.4mm and 3.6mm by layer height).

For version 2, I've increased the size of the numbers to print better, as well as improving some of the notch lines.  Also modified