Definition(s)
Vernier Calliper (or Dial Calliper)
Measuring device, usually with two legs or jaws, that can be adjusted to measure the thickness, diameter, and distance between surfaces. NOTE Vernier callipers have a vernier scale readout whereas dial callipers have a dial readout.
Source: API RP 5A5, Field Inspection of New Casing, Tubing, and Plain-end Drill Pipe, Reaffirmed August 2010. Global Standards