After I graduated from college I used one of these things extensively. In fact, I couldn't have survived without one! Many yearts later It's still somewhere around the house but hasn't seen the light of day for years! Nice treatment of an adjustable triagle. - Pops
When I left school I did a degree in Electrical Engineering. The first of the four years included a subject on technical drawing.
This is one of the devices we were told to buy, which I'm pretty sure I never used duing the course.
It is a fancy protractor, as Victor said, and was very expensive.
I think I might have used it a couple of times since then, but really I have kept it because of what it cost.