The «position indicator» is a type of protractor and is used for plotting on the nautical map of the observed angles from known land points.

The «position indicator» is used for the determination of the position of a ship (bearing) from horizontal angles between two or more objects, or of geographical features on land. The measurement of angles is done by another nautical instrument, which is called «sextant». The angles are drawn on the nautical map with the aid of the position indicator, and thus the position (bearing) of the ship is determined; it is also used for mapping coastlines.

This specific position indicator was manufactured in early 19th century by William Cary (1759-1825). Cary was an English manufacturer of scientific instruments; trained under Jesse Ramsden (1735-1800), Cary produced numerous scientific instruments, such as mechanical calculators, measuring instruments, telescopes, microscopes, navigation and research equipment. The instruments of William Cary were used throughout the world. After his demise, his company continued to manufacture nautical instruments until the mid 19th century.