As promised in a previous post, here is video of our 4-bit adder prototype. We used Wandel’s plans for it, but it is missing several niceties that Wandel’s version has: a top tray that holds marbles and releases them all at once, a bottom tray to catch the marbles, and a reset mechanism

Below are a couple of pictures of detail on the adder that I invented myself. When I first put the adder together, the toggles were not working well at all. After a good deal of thought I came up with the idea of putting a couple of paper washer behind each toggle. This solved the problem.

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