For those who like Sayers are unfamiliar with the back story, Doc only traveled a handful of times in the 85+ years of the strip. When he built the time-machine, Doc was already bald. He and his assistant, Jon, sent a camera back in time to get record events in the past. He accidentally left the time-machine on and transported Oop and Ooola to the 20th century. It would be quite a while before Doc took his first time-travel trip.