CIRCUMFERENTOR
Noun
circumferentor (plural circumferentors)
(surveying) An instrument used to measure horizontal angles, consisting of a brass circle and an index, all of one piece.
Source: Wiktionary
Cir*cum`fer*en"tor, n. Etym: [See Circumfer.]
1. A surveying instrument, for taking horizontal angles and bearings;
a surveyor's compass. It consists of a compass whose needle plays
over a circle graduated to 360ΒΊ, and of a horizontal brass bar at the
ends of which are standards with narrow slits for sighting, supported
on a tripod by a ball and socket joint.
2. A graduated wheel for measuring tires; a tire circle.
Source: Webster’s Unabridged Dictionary 1913 Edition