\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.