Posographe Analog Computer

by KAUFMANN, Auguste-Robert

c. 1922

98x139x12mm (cased posographe); leaflet 100x130mm; letter is a single sheet, 257x270mm

One of the most elegant analog computers ever made.

The Posographe is a photographer's exposure computer – one side works for indoor and the other for outdoor conditions. The user inputs various information – level of sunlight, colour of the walls, etc. – and the internal mechanism delivers an exposure time. In computing terms, the Posographe calculates two discrete functions of six variables each – all in a pocket-sized instrument without a single gearwheel.

This incredible piece of engineering was patented by Kaufmann in May 1922. This early example is accompanied by an important letter from the inventor, dated 1 September 1922. The letter is addressed to Maurice d'Ocagne, inventor of the Nomogram, and in it Kaufmann explains the Posographe and even sheds valuable light on how he created the brilliant internal mechanism.

Near fine condition: Posographe in its original case; fully functioning; leaflet very good; letter folded but very good.