<Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2007) (Learn how and when to remove this template message) </Td> </Tr> <P> Most projection booths in movie theaters in the past (and in some older theaters and studio screening rooms today) were equipped with two projectors side - by - side to project reels of film alternating between the two projectors . The cue mark was originally designed for such a setup . </P> <P> In such a system, the projectionist had a projector running the currently - playing reel (the outgoing projector) and a second incoming projector with the next reel to play, with each projector switching roles with each changeover . The projectionist would start the incoming projector with the changeover douser (shutter) closed as the first mark (the motor cue) appeared; the second projector would be threaded with the incoming reel parked 8 seconds of countdown ahead of the start of the picture section . The second mark (changeover cue) would alert the projectionist that the changeover was imminent, and one full second after the mark he would trigger a solenoid that would open the incoming projector and another solenoid that would close the outgoing projector . The audio would be switched at this time as well; the audio for a particular film frame appears 20 frames (about 15 ") before the image, and so all film prints carry the first two to three feet of audio of the reel they precede at their tail, called a sound pullup (digital systems use different offsets before or after the image, which a computer corrects for). Film prints could be prepped by a projectionist with automatic changeover cues, which were small metallic appliqués which could be applied to a print at the first cue mark . Readers attached to the projector would read the marks and execute the changeover sequence automatically, as long as the incoming reel was threaded properly on the second projector . </P> <P> However, most modern movie film projection systems have the film loaded on a very large horizontally - oriented platter (often colloquially known as a "cakestand"), in which all the reels of a movie are spliced together into one large contiguous wind of film filling the platter . Studios and preservation libraries that allow their archival or other rare prints to be exhibited typically demand that a twin projection system still be used so that their prints are not cut up for assembly . </P>

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