Nonius

Nonius, or vernier, is an instrument for reading fractions (usually tenths) of the smallest division of a given scale; invented in the 16th century by the Portuguese Pedro Nunes, and first constructed in its modern form in 1631 by the Dutchman Pierre Vernier. Nonius consists of a ruler that moves along the scale and is divided into 10 divisions, equal to 9 (first type) or 11 (second type) divisions of the scale. In both types of Nonius, each of its divisions differs by 0.1 from a division of the scale. In the second type of Nonius, the divisions run in the opposite direction to those of the scale. The nonius is brought close to the length being measured. Whole divisions are read off on the scale, and the number of tenths is equal to the number of the nonius line that coincides with a line on the scale. Examples of the application of Nonius - reading the height of a mercury column in a barometer, in calipers, cathetometers, etc. - A circular Nonius is used for reading fractions of divisions on a circular scale. The divisions of circular Nonii can be very diverse: the most common circular Nonii are those where 30 divisions equal 29 divisions of the scale, 20 divisions equal 19 divisions of the scale, and 10 equal 9 divisions of the scale. Examples of the application of circular Nonius - on the scales of spectrometers, saccharimeters, theodolites, etc.