so i have been thinking, if im measuring the runout or roundness or something else of a cylindrical object, i will put it in a v-block or two on the plate. i know nothing about v-block standarts, flatness of the surfaces, their "parallelism" (or whatever you call it), their roughness. are there any? does all this even matter or will a shaft somehow rest on three points in the block regardless of its accuracy. also when using two blocks i press the object into the blocks and thats it. now if i wanted to measure lets say to microns, maybe i should align the blocks with a parallel? but again, no idea how precise the sides are to the surfaces the piece rests on. or maybe the object also rests on three points in the two blocks and it doesn matter, unless the blocks were to move? well, a lot of question, it seems.