The Collaborative International Dictionary of English v.0.48:

Circumferentor \Cir*cum`fer*en"tor\, n. [See Circumfer.]
   [1913 Webster]
   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.
      [1913 Webster]

   2. A graduated wheel for measuring tires; a tire circle.
      [1913 Webster]