What this eight bit calculator can do is that it can do simple addition up to 128. It can also subtract down to 1. This redstone machine has 8 adders, 8 Pistons, 16 inputs, a subtraction system, a display, and can take up the space of 1-4th of the average learner plot. Another note is that the logic gates it uses are 40 NOT gates and 16 XOR gates.
In order to use the machine you must decide if you want to add or subtract. If you want to subtract, flip the lever down, but if you want to add, keep the lever up. The levers are labled A and B. If you want to add press A and B in any order but if you subtract, A must be a higher number.when you flip a lever, it corresponds to an input of a XOR gate. It does an equation by carrying over using redstone to another gate and outputting it into the interface or memory. If you decide to subtract, pistons will extend on to a 2 block inverter on every A block, making the redstone lamps light up. The lamp will light up if the answer is added and will darken if it was subtracted. There is also a display on the side showing what XOR gate it carried to. (example, if the answer was 4, it used XOR gate 3.) This does not apply to subtraction. Once you have inputed the numbers, the lamps will show the answer on the side. After your done, flip all the levers off and go again.