Just keep cutting a piece of stiff paper so it fits in any frame angle you need a measurement. When sides are touching along tubes get out your old school protractor and read angle. I use my adjustable drafting angle. I place it in frame till it touches both tubes. than read angle About $10 at a drafting tools supply place. Has your not going to be reading many frame angles both work great For tube diameter I just use my pipe wrench with parallel sides and tighten on tube. I take off and measure diameter. Charles Nighbor Walnut Creek, CA.