Mechanical Programme Finder for use with 45 degree Prismatic Astrolabe, by Cooke, Troughton and Simms

Box containing Mechanical Programme Finder (a type of planisphere) consisting of duralumin alloy disc and ten celluloid quadrants; ‘Star Catalogue for 45° Prismatic Astrolabe’; and diagram of ‘45° Astrolabe Value of Coefficient “A”, made by Cooke, Troughton & Simms, York, England, UK, 1930-1940. Designed as an accessory for use with the 45° Prismatic Astrolabe, also manufactured by Cooke, Troughton and Simms. Diagram corresponds to Diagram No. 5072 in the Star Catalogue.

This Mechanical Programme Finder (a type of planisphere) and its associated materials were manufactured by the British firm Cooke, Troughton & Simms as an accessory to their 45º Prismatic Astrolabe. From the 1930s, surveyors used the planisphere to calculate latitude and longitude (and thus determine their exact position on Earth) from the positions of stars observed with the Astrolabe. Recorded users of the Astrolabe include the U.S. Hydrographic Office (e.g. in Venezuela) and British imperial surveyors (e.g. in Canada and East Africa).