The angle measurement is the same at any point on the line. (try this with a regular 8 1/2 x 11 inch paper). With a sharp pencil, draw a 1/4 inch line along the bottom and one side of the paper. I find it is easiest to take a corner of that piece of paper because I know it is a real right angle. So put the center point on the corner of the paper where the two lines you have drawn, intersect.(the 90 degree line should go on the line up the side of the paper) and the horizontal on the line on the bottom of the paper. Now, mark your degree. Take away the protractor, and draw a line from the corner THRU the degree mark and continue as far as you want. That's it. If you don't care about seeing what is under your ruler, you could actually use the paper template as is, and just lay your regular ruler over top to cut.
Hope this helps.