a small movable scale running parallel to the main graduated scale in certain measuring instruments, such as theodolites, used to obtain a fractional reading of one of the divisions on the main scale
2.
an auxiliary device for making a fine adjustment to an instrument, usually by means of a fine screw thread
3. (modifier)
relating to or fitted with a vernier
a vernier scale
a vernier barometer
Word origin
C18: named after Paul Vernier (1580–1637), French mathematician, who described the scale