Mechanical calculators are an engineering marvel unknown to most people. The most advanced mechanical calculator ever built, the Curta calculator, fits into the palm of your hand and uses to perform addition, subtraction, multiplication, and division.
Each Curta is an incredible piece of art, but so few exist that one in reasonable condition can cost thousands of dollars. Instead, one man decided to make his own. Using 3D-printed parts, Marcus Wu built a 3x scale model fully functional Curta.
Adam Savage got his hands on one in this recent video:
If you want a 3D-printed Curta calculator of your own, you can to find all the instructions to print the parts. Just be aware that there are more than 300 parts involved in the calculator so assembly is not going to be easy.