Wild D13 Distomat electronic distance measuring apparatus (EDM). The apparatus comprises a distance measuring head (capable of being attached to a theodolite); microprocessor and display unit; battery pack; interconnecting cables; reflectors (with mounting pole). The microprocessor unit is designed to be located in a standard tribrach; it also has a composite tribrach on its top for mounting a compatible theodolite.
For the tripod see https://ice-museum-scotland.hw.ac.uk/product/1997-001-1/.
This device operates by transmission of an infra-red radio signal reflected by a dedicated target prism interpreted by a microprocessor unit which displays in a digital format horizontal, vertical and slope distances. To enable these distances to be calculated horizontal and vertical angles are read from the theodolite and tapped in by appropriate use of numbered levers. This D13 model is an early example of electronic distance measuring equipment. A later D13S model replaced the numbered levers with a digital key pad on the top of the microprocessor unit. Because of its weight and bulk the D13 (and the D13S) was cumbersome and difficult to move around in the field. The D13 series was superseded by the more transportable and less cumbersome D14 model.