These bits are computed in the following ways. First, the carry bit is the final carry out of the adder circuit. It also stands for overflow when the two values that were added are considered to be unsigned binary numbers, not 2's complement signed binary numbers. Thus, the C bit is sometimes called unsigned overflow.

Next, the negative bit is nothing more than the output of the MSB (most significant bit) of the adder.

The zero bit indicates whether the result of addition is 0 or not. The computer feeds all the outputs of the adder into a big NOR gate (or a cascaded series of ORs followed by a NOT). If any wire has a 1, the output is 0. But if all the wires have 0s, the output of the NOR is 1. The use of 1 to indicate "zero" is a bit confusing since we might expect 0 to be on the 0 wire. However, think of 1 as true and 0 as false. So if Z is 1, then the Z condition is true, namely that the output of the adder is 000...0.