Algodoo

Completely mechanical.
Somewhat laggy.

Press shift to read and act upon next card. Adding and subtracting takes awhile so make sure everything has stopped moving before pressing again.

I worked on this for ages, but for some reason it doesn't add properly on certain numbers. Don't know why, got too burnt out to care. Seems to work fairly well on the numbers I have currently. Figured I'd post since people may get a kick out of it. Breaks occasionally.

Rod logic adder-subtractor with three 8-bit registers. Results can be transferred back into register 1 or 2 for further calculations.
All numbers and functions are controlled by "punched cards". Card codes included in scene.

7 cards preloaded:
put 00101101 in register 1
put 00100111 in register 2
add together (= 01010100)
move results to register 1
put 01000111 in register 2
subtract reg2 from reg 1 (= 00001101)
clear all registers

Instead of using eight full adders-subtractors I use just one, which reads each bit stored in the registers one at a time, loads the sum into the Results register, stores the carry, and then cycles to the next bit.