Presenting Kaufmann’s Posographe, a wonderful device, reducing a series of nomograms to a single complex linkage.
Kaufmann’s Posographe - a pocketable analog exposure calculator
At first glance this is just a small rectangular plate, about 13 x 8 cm, covered with dense scribbles, with seven pointers fixed to its frame. Then you realize that the pointers are not fixed, but can slide on the frame… and then you note that they are somehow interconnected – moving any of the small ones will move the larger one this way or that… Kaufmann’s Posographe is nothing less than an analog mechanical computer for calculating six-variable functions. Specifically, it computes the exposure time (Temps de Pose) for taking photographs indoors or out (depending on which side you use). The input variables are set up on the six small pointers; the large pointer then gives you the correct time. The variables are very detailed, yet endearingly colloquial
via Nate Steiner