Historical information

The Plane Table Alidade was used as the sighting Instrument in the production of historical manual hand drawn maps. A Plane Table Board mounted on a tripod is levelled and the Alidade is placed on the table with the vanes perpendicular to the it. Each sighting vane has a central thread lined up on the target and the angle to that target point is then drawn on the map sheet using the beveled fiducial edge. Plane Table Surveying is used as a quick method where less accuracy is required or needed. Plane table Surveying is a relatively portable and inexpensive method and was used extensively before the advent of sophisticated surveying instruments. The photo at 6489.2 is an Australian Army Survey Corps Party using a Plane Table Alidade in Syria during WWII.

Physical description

Two Plane Table sighting instruments (Alidade) used for historical manual map making housed in wooden transit boxes. A brass instrument with folding sights at each end and a beveled fiducial edge in one edge. The front sight is the object vane and the rear sight is the sight vane. There is a sliding arm attached to the base to draw parallel lines to the fiducial edge. Very slight differences in model between these two instruments.

Inscriptions & markings

First Instrument, "ER Watts and Son, London, 1938, MkII, Box Label 423. Second Instrument - R. E-Co, Mk.II, stamped E686, Box Label 686.