When more precise measurements of length are needed than can be obtained with a ruler, yardstick or tape measure, a Vernier caliper is used. These calipers are used in laboratories and manufacturing applications.
According to the Britannica Online Reference Center, this device was invented in 1631 by Pierre Vernier, whose hobby was mathematics. Vernier was a government official in France during the 17th century.
Vernier calipers use two parallel scales, a main and a vernier. The scales are in inches or metric. Divisions on the vernier scale are one more than the main scale, gaining one more digit in accuracy.
The main scale is fixed and the vernier one moves. Using both the main scale and the vernier provides measurements either in inches and tenths of an inch or millimeters and tenths of a millimeter.
Measuring tolerances in scientific settings often require more precision than simple rulers can give. Manufacturing specifications for small parts may be smaller than a millimeter. For even smaller measurements, Vernier micrometers can measure ten-thousandths of an inch.
The name Vernier meant someone who lived near an alder tree. It is a derivative of Varnier or Warner. In the U.S. most of the Vernier's settled in Ohio and Michigan.