Parallel (or drafting) ruler #freecycle

Used parallel or drafting ruler. Multi-function. Has a protractor, reference equations, angles with cos and sin equivalency. I think rolling part is supposed to be good for drawing parallel lines, but somehow it's upside down (so the measurement is on the other side where it doesn't have a tick mark). I don't know if you can easily take out the rolling part and put it the right way without breaking it. I'm not so familiar with this ruler