Minecraft wiki entry for Calculator, associated text: The white machines are half-adders, that use, as inputs, the carry of the last adder and the sum of their respective full adder. We need this because, if the answer is negative, it uses the equation " -A = !A (inverted A)+ 1 ", as explained here. The final outputs are all of the top-most wires you can observe, plus the wire on the right (the carry from the last full adder) and the carry that goes in the first (left) half-adder, as the negation sign.