Apparently it runs fast enough to be programmed interactively. Keyboard input via mechanical linkages is a solved problem: consider the humble typewriter. The Selectric typewriter even had macroscopic digital mechanical "circuitry"; each keypress moved a lever with lugs that encoded a binary code specifying coordinates for where on the typeball the character was located, and special linkages called whiffletrees converted the digital code into analog rotations for the typeball mechanism in the manner of an R-2R ladder or similar in the electronic realm.
The idea is that the CPU and peripherals would communicate via mechanical linkage (say, levers moved, or not moved, according to whether the signal is "high" or "low") rather than electronic voltage levels on a wire. For some peripherals, electromechanical adapters could be built that use relays to convert electronic signals to mechanical ones and back, allowing you to theoretically even plug in standard PC keyboards and displays into such a mechanical computer.
The idea is that the CPU and peripherals would communicate via mechanical linkage (say, levers moved, or not moved, according to whether the signal is "high" or "low") rather than electronic voltage levels on a wire. For some peripherals, electromechanical adapters could be built that use relays to convert electronic signals to mechanical ones and back, allowing you to theoretically even plug in standard PC keyboards and displays into such a mechanical computer.