The Collaborative International Dictionary of English v.0.48:
Circumferentor \Cir*cum`fer*en"tor\, n. [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 360[deg],
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.