Definition

Pivoted sight bar that moves over a graduated arc. The upper part of a THEODOLITE. The alidade used in topographic SURVEYING consists of a straight-edge ruler carrying a TELESCOPE or other sighting device and used in recording a DIRECTION on the plane table sheet. The term is also used to describe a BEARING CIRCLE fitted with a TELESCOPE to facilitate OBSERVATION of BEARINGS. If a TELESCOPE is used, the instrument is often termed a telescopic alidade.