Wild Heerbrugg ST4 Mirror Stereoscope: an enameled (khaki green) metal stereoscope with four legs, clear optics and surface-silvered mirrors encased in a wooden case with green velvet lining and a strip of sponge in the lid. Included is a pack with a white lens cleaning cloth and an instruction manual stamped 31 Jan 1978. 'P.C.C. Engineering Dept.' written on lid of case outside.

The object came from City Assets and Environmental Sevices Dept. at 1A Civic Place before it was to be demolished.

The ST4 instrument is unmatched for precision and ease of use for viewing and interpreting aerial photography.

From instruction manual:

The Wild ST4 Mirror Stereoscope is an instrument for three-dimensional viewing of stereoscopic picture pairs. A satisfactory spatial image can be obtained from almost any pair of pictures showing the same object, as long as both pictures show the object in the same attitude and relative position, at nearly the same scale (apparent size), from exposure stations not too far apart and facing approximately in the same direction.

Mirror stereoscopes are used cheifly in the interpretation of aerial and terrestrial photographs and as auxiliary instruments in all phases of surveying and mapping.

Stereoscopic vision is obtained by looking at an object with both eyes. The left eye sees a slightly different picture from that seen by the right eye; both pictures are fused by the visual centre of the brain into a three-dimensional impression of the object.