straightedge

A straightedge. Plastic one isn't necessarily the best for much of anything, but nonetheless, if you print this, at least you will find out if your printer prints skewed. Mine does. The result was about 2 mm off at the edge of the shorter part. It amounts to a total of 2 or 3 degrees off.

So. I don't recommend this to be printed on cheap diy printers. The good ones should make an actual useful straightedge. Please if you print this post a comment, i'd appreciate it.