The films are termed “single concept” because they run for only about five minutes and deal with a single theme or topic. However, the film can be played continuously with unlimited repetition without rewinding or even stopping the project. Because of the high magnification and the positioning of the camera, the image on the screen (19in x 15 in) gives a much clearer picture to a larger number of pupils than can be obtained by demonstration at close rang, there being no distortion at the edges and the picture being clearly visible from every angle so that every student sees every demonstration clearly. The film can be stopped and the picture retained at any frame , and on the 20in “ stop-frame” remote control lead a constant focus is maintained. To eject the cassette the lever at the rear is pressed and the cassette springs out.