Synch/Desynch
I can't speak for wartime practices, but I do know that flying for any length of time with the engines desynched was most uncomfortable, as the whole aircraft would vibrate and the rest of the crew would shout at you (or worse). Although it could be done by looking at the props, at least on Avro's finest there was a 'synchrometer', and all you had to do was fine tune the RPM until the little prop indicators stopped moving.