This is the best mechanical (occasionally steam-powered) computer you’ve seen today. Inspired by the theories of Alan Turing, the British mathematician and Enigma code breaker, Jim MacArthur took it upon himself to build a Universal Turing Machine out of scraps.
The machine uses a metal grid with ball bearings as its memory, moving back and forth over the bearings and repositioning them as necessary. According to MacArther, if the tape to be extended to an infinite length, it could conceivably solve any computation.
Originally conceived by Turing as a thought experiment to explain the operation of computers, MacArthur built the device with an eye toward being completely analog. While it can be driven by hand, an electric or steam-powered motor needs to be used for longer computations.
Sure, it could conceivably take months to add two numbers together. But who cares: it’s a computer that uses ball bearings and can run off a steam engine. A true marvel of the tinkerer’s art.