The Rebuild of Colossus

A closer look at the logic circuits. These perform a Modulo 2 addition,(XOR), just like the relay circuits on the German Lorenz cipher machine. ( 0 + 0 = 0; 0 + 1 = 1; 1 + 0 = 1; 1 + 1 = 0; )
Beneath the logic panel is the master control plate. This was very difficult to re-create and get working. No circuit diagrams survived. But Tony Sale based it on a surviving master control circuit for Super Robinson and eventually it worked.
It provides the pulses within the blank tape join interval to dump the counts, reset the counters, set the rings to a new start point and start the rings and counters for the next pass along the cipher tape.