This is a 1:25000 Navigation Protractor, similar what's used for land navigation in the US Military.  This is made to work with UTM overlays on 1:25000 scale maps, which can be easily generated with Cal Topo.  Used in conjunction with a compass, this is what one would use to plot a course at the infantry level.  Can also be used on a 1:50000 scale map, you'll just use half of the scale instead of the full.  

Land navigation is a lost art, but your local infantry guy will know what this is, and it's something our children should know too.  Check out some youtube videos on the subject and take a dive into Land Navigation.  One my favorite things I did while in the service.

Print using 0.2mm nozzle because of the fine details.  Use PETG if you expect it to be in sunlight a lot.  Which, you know, you should.