Really, this is tied to my fascination with mechanical calculation as a whole. There's a whole art out there of computing things using the physical motion of objects, which (until the invention of working electronic computers) had tremendous practical significance -- that's everything from a slide rule or an abacus up to the incredibly intricate and beautiful Curta calculators of the 1940's-70's. (https://www.youtube.com/watch?v=loI1Kwed8Pk) At the extreme, it was used to build full-scale computers, like the fire control computers used in ships. (https://www.youtube.com/watch?v=s1i-dnAH9Y4)
The realization of mathematics in physical objects is beautiful.
Via and .