Matthias Wandel’s webpage describing his “binary marble adding machine” includes a YouTube clip as well, but for math geeks, the point should be clear from the above. Dropping marbles from the top of the gadget changes the state of the little toggles (a.k.a. “flipflops”), trapping some marbles and allowing others to fall through. Very kewl.

And one of the only physical demonstrations of binary addition I’ve ever seen. I mean, sure, there are applets online that will show you how to add binary numbers, but the wooden example above feels to me like a step that will bring you closer to understanding something like a circuit description of a binary adder. Perhaps someone with more intimate knowledge of computer circuits could draw some parallels… Do the wooden “flipflops” correspond to XOR gates?