thanks for all the input! although i love and appreciate nice tools, for something i'll use so infrequently i think the $75+ ones are overkill.

analog at low cost doesn't look like it has enough precision. given that the entire lifespan of the rotors is .3mm (1.8->1.5), i think i'd at least like to believe i was measuring more accurately than .1mm! i'll go with a mid-level digital one and report back if it tells me my rotors are 3mm thick