nonius
/ˈnəʊnɪəs/noun
A device consisting of a series of concentric arcs engraved on a quadrant, used for the accurate measurement of angles, altitudes, and heights. Also (in full nonius quadrant): the quadrant itself; also called pantometer. Frequently attributive Now chiefly historical.
- The nonius was superseded by the vernier, with which it has sometimes been confused..
Origin
Mid 18th century; earliest use found in Philosophical Transactions of the Royal Society of London. From post-classical Latin Nonius, Latinized form of the name of Pedro Nunes, Portuguese mathematician, who invented this device and described it in his work De Crepusculis.