I found a small notebook from WWII which has handwritten instructions by the R.A.O.C York for a few projectors and some extra information. Slowly all the information from the botebook will be added to the site. This is information on 16mm sound films.

Sound films

By R.A.O.C. York. Circa. 20-25/10/40

Sound films are easily recognisable from silent, as 16 m.m. Sound films have one set of perforations only. Sound films must not be projected from a Kodascope or other silent projectors. The sound track of the film is of two types. 1. Variable density. 2. Variable area.

Size of sound track :- .06” wide.

Projection speed of sound film is 24 pictures per second.

1 ft. of film takes 1 2/3 seconds to be exposed.

There are 40 pictures per foot of film.

Sound is always 25 pictures in front of corresponding picture, to allow for the threading in the machine.

Projection speed of silent film is 16 frames per second.

Fig. V THE TWO TYPES OF SOUND FILM.

A VARIABLE DENSITY
B VARIABLE AREA.