An additional bit that can mess with things is that the cutter head's rake angle isn't a certainty!
A cutter stylus lasts about 10 hours of cutting. It has to be heated for best noise floor; as it wears it gets noisier and the temperature has to be adjusted but eventually it simply has to be changed out.
To do that the cutter head is removed from the lathe and the stylus is replaced. Then the head has to be set up again- to get the stylus to the proper position, depth, etc. Once that looks right, then test recordings can be made. Its right when the groove is completely silent. And by 'silent' I mean so quiet that literally the playback electronics are the noise floor.
At no point is there a measurement of the rake angle. The engineer is setting up for *lowest noise* and not anything else. Each stylus is a bit different, so after replacing one the engineer might have to do a bit of head scratching to get it right again. So that whole 92 degree thing is an approximation; its not cast in concrete and every LP is slightly different on this account.
IMO (I own a Scully lathe with a Westerex cutting system) this is a thing that isn't worth your worry. About the only thing that the microscope might be good for is making sure that the stylus is indeed on the end of the cantilever in the first place and that its not at a weird angle and so on- that you **will** be able to set it up in your arm.
