I have seen Vernier Calipers which were graduated to both .001" & 1/128" (.0078"). I much prefer my set graduated to 3.001" & .02mm (.00079"). If its closer than that I want something besides a caliper to measure it, matters not if its vernier, dial or digital.
In one shop I worked in we had a large bench micrometer we called a Super mic in inspection. It was set to the desired measurement or very close to it with gauge blocks while looking into a window. As you put pressure on the anvil by turning the thimble there were light beams visible in the window you watched to see bend so constant pressure was always maintained taking "Feel" out of the equation. I ground some small pins once which were checked on this machine, after being brought to a stable temp, which had a tolerance of +.0002", -.0000".
I had a much older machinist once tell me that while working in a railroad shop he once had the turn some parts for a interference fit with some pre,bored mating parts. All the measuring tools they had to do this with were large inside & outside spring joint calipers. He set the inside calipers to the hole then the outside ones to them. To get the fit he held one leg of the outside calipers against the bottom of the part & measured how far across the top the upper leg "drug" as it was pulled over center. As best as I recall the part was some 12"-14" in diameter & he had to get a Ľ" "Drag". Some of the oldtimers dis amazing work with limited tooling, but they didn't Spit it Out at the speeds expected today.
