Very common to plate check part with only a set of jo blocks and an indicator to a height gauge. strike the part/move an inch or half and strike again.
I used to make angle parallels on the surface grinder so that could be attached or held to a fixtured part and so check an angle with not taking a part out of a set-up.
With a machine that you can trust the travel dials one can just use the machine to trianglate movement with an indicator held... to hit zero/move travel/ hit zero again.
one degree is near a mile so not that hard to check.
15* s =.259 cos .966 Tan .268
14* S.242 cos .970 tan .249
16* S .276 c=.961 Tan =,287
I think, check your book. (I don't have my book handy so check my numbers)
About half the difference will be half degree so that might be your check.(about.008.009 for half degree.)
(Actually a half degree is not difficult to see with a hand held protractor.)