To measure angles including frame angles go to a drafting tools and purchase an adjustable drafting angle. Just put into angle to be measured. Adjust so both edges of triangle touch opposite sides and read the angle from the degrees printed on the triangle. As an architect I used one many years drafting construction documents plans of many a building. What is tougher to measure is the total desgn measurements of a frame. I went to Ed Litton frame and paint shop in The Bay Area today and Ed was nice enough to show me many of the 40's, 50's ,60's, 70's, and 80's (and beyound which I can't mention on this chat line. What a history these frames could tell if only they could speak. Charles Nighbor