Enclosed is a copy of a heavily modded version of DF 40d, with a save containing an 8-bit adder/subtractor calculator based on the logic sketched out by Jong in this thread. It calculates the correct answer instantaneously upon receiving the input, with the only lag in the system being the response time of the output pressure plates. Addition is simple binary addition, subtraction is twos-complement binary subtraction.

Note: the modding mostly pertains to the dwarfs being more effective workers (they move much faster and require no food, drink, sleep, entertainment, or even air, and can conjure steel, fuel and wood out of thin air at smelters and forge steel mechanisms). This allows me to build large mechanical contraptions easily to see if they work properly (or at all).