Telerecordings of Doctor Who episodes were made during the 1960s and early 1970s so that episodes could be sold to overseas broadcasters. At that time, many overseas broadcasters didn't possess the technology to broadcast the videotape on which the British Broadcasting Corporation recorded. Thus, Film Recording Clerk Pamela Nash and her staff would oblige overseas clients by making a master 16mm negative of the episode and then burning off prints of that episode as requested.