This Add-Subtract Module (ASM) was created for the 1997 Reconstruction of the Atanasoff-Berry Computer (ABC) and is a copy of one of the 30 parallel ASMs used in the original 1942 computer. Its seven dual-triode vacuum tubes (6C8) combined two bits and a carry/borrow bit to produce a sum or difference bit and a carry bit. Each ASM operated serially on a 50-bit number from right to left, producing a binary result accurate to 15 decimals.
