When I was in high school, my math teacher showed us an easy way to indicate angles. She simply fastened two see-through plastic protractors on top of one another. I’ve used this simple devise to draw and check angles in my workshop ever since.
Start with a pair of identical protractors from an office supply store (about $1 each). Carefully drill out the center holes to exactly fit a 6-32 x 3/8-in. flat-head machine screw. Next, drill a countersink for the screw head in the bottom protractor, so the protractor sits flat for drawing angles. Install the screw and nut, making sure the protractors are precisely aligned. During use, the top protractor’s zero line indicates the angle on the bottom protractor’s scale. The angle matches the opening, because the bottom edges of the protractors are parallel to the zero lines.