vernier

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A small, movable auxiliary graduated scale attached parallel to a main graduated scale, calibrated to indicate fractional parts of the subdivisions of the larger scale, and used on certain precision instruments to increase accuracy in measurement. Also called vernier scale.
2. n. An auxiliary device designed to facilitate fine adjustments or measurements on precision instruments.
3. adj. Of, relating to, or having a vernier.

Century Dictionary and Cyclopedia

1. n. A small movable scale, running parallel with the fixed scale of a sextant. theodolite, barometer, or other graduated instrument, and used for measuring a fractional part of one of the equal divisions on the graduated fixed scale or arc. It consists, in its simplest form, of a small sliding scale, the divisions of which differ from those of the primary scale. A space is taken equal to an exact number of parts of the primary scale, and is divided into a number of equal parts either greater by 1 or less by 1 than the number that it covers on the primary scale. Fig. 1 represents the vernier of the common barometer for measuring to the hundredth of an inch. The scale is divided into inches and tenths of inches; the small movable scale is the vernier, which consists of a length of eleven parts of the main scale divided into ten equal parts—each part being therefore equal to eleven tenths of a division on the main scale, and the difference between a scale-division and a vernier-division being one hundredth of an inch. To use the vernier, the zero or top line of it is set to coincide with the top of the barometric column, which in the figure stands between 30.1 and 30.2 inches. If the zero of the vernier were set to coincide with 30.1 inches on the scale, the first division would be one hundredth of an inch below 30 on the scale, division 2 two hundredths below 29.9, and so on, division 10 coinciding with 29 inches. Hence, as the vernier is raised its divisions coincide successively with scale-divisions, and the numbers on the vernier correspond to the hundredths it has been raised. In the figure the coincidence is at the seventh vernier-division—that is,the vernier stands seven hundredths of an inch above 30.1, and the height of the mercury is therefore 30.17 inches. Fig. 2 represents part of the limb of a sextant with a vernier. Also called nonius. See also cuts under caliper, square, and transit.

Wiktionary

1. n. A secondary scale with finer graduations than the primary scale of a measuring device; the vernier measures between graduations of the larger scale.
2. n. A secondary control input with finer control than the primary, or coarse, input; for example the vernier frequency tuning knob on a radio.
3. n. physics A secondary system of force application for the attitude control of a spacecraft; for example a vernier thruster.

GNU Webster's 1913

1. n. 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.

WordNet 3.0

1. n. a small movable scale that slides along a main scale; the small scale is calibrated to indicate fractional divisions of the main scale
2. n. French mathematician who described the vernier scale (1580-1637)