I have no problems at all measuring firing pin hole centers using a set of calipers. Matters not if they are Vernier, Dial or Digital except as to how they are read. Vernier's are the hardest to read but have the advantage of having nothing what-so-ever to get out of adjustment. I still have 2 or 3 vernier calipers from my machinist days which I use rather frequently. Also have a 6" Starrett Dial caliper which I use a lot for the ease of reading with my Old Eyes.
The calipers all read to .001" while the smallest graduation I recall ever seeing on a machinist scale was .010" so a bit of interpolation is need if you want it closer than that. If the scale is all in fractions, which many are, then the smallest increment is normally 1/64" (.0164"). I can Certainly read it closer than that with calipers.
