This is a calculator that can take 4 bit inputs and output 8 bits. It features an adder, subtractor, and multiplier. The color code for the calculator is, Green: Adder, Red: Subtractor, Blue: Multiplier, Dark Gray: Decoder, Yellow: 7 segment display encoder, and misc. wiring. I used either simple concepts found online, or what I could think of to build this calculator. This is the reason why the methods I used are outdated and inefficient (especially with the 8 bit decoder). The calculator takes around 3 - 10 seconds depending on how large the number is (larger numbers take longer due to how the 7 segment display encoder works).
There are two rows of levers and 3 buttons. You use each row of levers to select which numbers you want to input. So the top row would be input A and the bottom row would be input B. For subtraction row A is being subtracted by row B. You can press whichever button that corresponds with its sign to select which operation you would like to use. Note that you do not need to select a operation button each time you want to calculate anything, it is only needed if you want to change your current operation. The display will show which operation is currently being used. Example: To do 7 - 5, simply flip the 7th lever on the top row, the 5th lever on the bottom row, and press the subtraction button if the operation has not already been selected.