Kaufmann’s Posographe is an intricate pocket-sized mechanical calculator invented back in the 1920s. Measuring 13x8cm and filled with tiny scribblings, the device allowed photographers to approximate the exposure values they needed by simply sliding around six small pointers.
Here’s a look at the front and back of the Posographe, along with a diagram of its innards:
Technology has come quite a long way since then, eh?
Kaufmann’s wonderful Posographe [History of Computing]