The ALU can do addition, subtraction, multiplication, division, modulus, and square root with two 8-bit signed integers. Signed means that the left bit says whether the number is positive or negative while the other 7 bits are used for the calculation. The adder/subtracter uses two ripple adders and some XOR's to add two positive or negative values together. Setting the function to subtract simply inverts the sign of the second number before the calculation. The multiplier, divider, and square root extractor are all sequential, so they use shifting and conditional logic similar to how you would normally do binary multiplication, division, and square root by hand.
The machine is used by inputting the values with the levers in front and then hitting the green button to start the calculation. The red levers set the value for A, and the blue levers set the value for B. Two levers for A and B (which are labeled) set whether they are positive or negative. The magenta levers set the function to calculate in binary. A list of the functions with their corresponding values are listed near the left of the machine. Once the green button is hit to start the calculation, it will start calculating and the green light in the back will pulse at the same time a noteblock sound is heard which signifies that the calculation is done. The answer is read while facing south to see the bits in the correct alignment. It was designed this way so that it can be easily used in a CPU where you wouldn't want to flip the result. The yellow lamps give the whole number value from 0 to 127 while the light blue lamp says whether it is positive or negative.