I wanted a ruler that was the right size to use in sketching my ideas on a clip board. I found thingiverse.com/thing:1888

It was close to the right size but it had protruding surfaces that were awkward if the ruler was flipped over when sketching. The length was a bit too long to fit on my print bed too.

This ruler is 132mm long and has cm tick marks on the top and bottom of the ruler. It also has a 45 deg angle on one end and a 60 deg angle on the other.

This is my ideal sketching tool. My neighbor saw it and asked that I would print some off for his kids.

(UPDATE) I decided that I like the ruler better without the notches on the back side. I didn't use them and they tended to get in the way when tracing a straight line. Check out version two. :)