vernier
vernier
(ˈvɜːnɪə
) noun
1 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
[C18: named after Paul Vernier (1580–1637), French mathematician, who described the scale]
