https://i.redd.it/069dh87ukp1e1.gif

I've designed a simple mechanical calculator that does addition and subtraction up to a maximum output of 20!
It was a little tricky to figure out where the numbers should go on the scale but the result is quite satisfying to play with.

I think it was the first time I had to use the trigonometric identity sin(a+b) = sin(a).cos(b) + sin(b).cos(a) ever since I left high school. It took me a while to remember this existed!

If you like it, you can download it here: https://www.printables.com/model/1057622-math-balance

All feedback is appreciated!