The Circumferentor was an early theodolite. It was a large compass with a swivelling dial. A metal gunsight groove was used for sighting on distant objects or on progress lines. The dial could be adjusted to record a bearing from magnetic north and then to determine the angles to sighted objects. The instrument was mounted at eye-level on a pole; a ball-and-socket joint eased the swivel. It was a very innacurate instrument

Dec. 2012                                               Last updated May 2015