Acmade 16mm film edge numbering machine.
A film edge-numbering machine was an essential part of any film cutting room. Sound film 'rushes' came to the editor as two separate reels - the pictures on film and the sound on magnetic sound film. The first task of the editor's assistant was to synchronise the individual shots on the film with the related sound on the sound film. This was done by aligning the frame showing the moment the clapper hit the clapper board with the frame on the sound track where the bang started. The two films were then clamped in a synchroniser and cut to the same length, then the next shot was synchronised, added to the roll, cut to length and so on, through the roll. As the clapperboard was cut off in editing, and both film and sound tracks were likely to be cut and reassembled in various ways during the editing process, it was vital to be able to ensure that every shot remained in synchronisation. A visual confirmation of this was most useful. This is where the edge-numbering machine came in. Once the rushes were synchronised, each film reel and accompanying sound reel would be put through the numbering machine. The picture and sound films would be set up to start at exactly the same frame (ie 'level sync') and run through the machine so that identical but incremental numbers were printed in white ink along the edge at regular intervals on the two rolls. Different sets of numbers were printed for each pair of rolls. In this way, the editor could check that sound and picture were always in synchronisationat at any stage in the editing process, which could take weeks.