8mm was a standard film format, so named because of its 8-millimetre width. As such it was the smallest of the major film sizes, and never used by the production staff to record Doctor Who. However, because it was cheaper to buy and develop than 16mm or 35mm, it became the medium of choice for "home movies". Over the years, several people, sometimes only vaguely connected with the production of Doctor Who, would take 8mm home movies of the recording of Doctor Who — particularly location filming. For several missing episodes, 8mm recordings of filming give vital insights into what the production may have looked like.