They also had to be spliced to long leaders if the film was going to be shown on multiple screens...a friend of mine owns several local theatres, and they only received one copy of each film, to a long leader was run through all the projectors in the projection gallery that would be showing the film, the leaders determined the start times for the movie, if one started at 8pm and the leader to the next projector was 13 minutes long the second screen showing would start at 8:13pm, imagine the leader for 10 screens, there were guide pulleys for the films all over the gallery to allow the film to line up with each projector in the sequence.