from
The Collaborative International Dictionary of English v.0.48
Vernier \Ver"ni*er\, n. [So named after the inventor, Pierre
Vernier.]
A short scale made to slide along the divisions of a
graduated instrument, as the limb of a sextant, or the scale
of a barometer, for indicating parts of divisions. It is so
graduated that a certain convenient number of its divisions
are just equal to a certain number, either one less or one
more, of the divisions of the instrument, so that parts of a
division are determined by observing what line on the vernier
coincides with a line on the instrument.
[1913 Webster]
{Vernier calipers}, {Vernier gauge}, a gauge with a graduated
bar and a sliding jaw bearing a vernier, used for accurate
measurements.
{Vernier compass}, a surveyor's compass with a vernier for
the accurate adjustment of the zero point in accordance
with magnetic variation.
{Vernier transit}, a surveyor's transit instrument with a
vernier compass.
[1913 Webster]