This something I made to draw circles quickly. I think the right word would be “a pair of compasses). Correct me if I’m wrong :-).
The Idea is that the center can be hold down by hand and the rules can turn around it. In the holes you can stick a ballpoint of pencil. The big holes (2mm) on the red ruler are 10mm apart from each other. The small holes (1mm) are 1mm from each other. The blue ruler has only 2mm holes that are 5mm from each other.
The Centre has a scale divided in 10° segments but also in 0, 22.5, 45, 65.5, 90 etc. With this scale it’s possible to make quarter circles, for instance...
In the center you can fit a 3mm drill, rod or pointy object that can be fixed with an M3x10mm bolt and nut.
Printers: Customs & Anets
Design Programs: 123D Design, Inkscape, MeshMixer