In 1631 French mathematician Pierre Vernier (1580-1637) published a mathematical treatise showing that a small, movable auxiliary scale could be attached to a larger, graduated scale to obtain finer adjustments. From that beginning developed the vernier scale, a short, graduated scale, or ruler, that slides along a larger scale. The subdivisions on the short rule are nine tenths as long as the subdivisions on the long scale, and the scale can measure both lengths and angles.
Engineers often use calipers with a vernier attachment. Some of them read to one thousandth of an inch without a magnifier. The vernier scale which divides each unit of the larger scale into smaller fractions is used with such instruments as the transit, sextant, quadrant, barometer, and compass, as well as the caliper.
To grasp the fineness of the measurements made possible by the vernier, consider this: The beam of a caliper is divided into inches and tenths, and each tenth into fourths. The vernier is divided into twenty- five parts. Sometimes the beam is divided into fiftieths of an inch, and the vernier has twenty divisions to each nineteen divisions on the beam.