YouTube archivists WDTVLIVE42 have unearthed “Threading the RCA Projector”, a 1950s instructional film showing viewers the proper way to operate a 16mm projector. The film, which was was produced by the State University of Iowa, is “one in a series on the use of audio visual equipment.”
To rewind the film after a showing, bring the end of the film to the feed reel and attach it. Wind counter-clockwise a few turns to take up the slack. Turn the rewind lever to rewind. Turn on the projector switch and let the projector run until the film is rewound.