Journal of the Society of Motion Picture Engineers (1930-1949)

214 WALTER H. CARSON [j. s. M. p. B. are particularly popular for practical use. The first one is not commonly known, and the other two require instruments of a type not usually available to the film laboratory or exchange. It was these facts which led to the introduction of a perforation pitch measure by Agfa, which, by its size and convenience of use, makes it pitch measure FIG. 1. Perforation pitch measuring rule. possible for the cameraman, laboratory operator, or inspector in the film exchange to check the condition of a film as regards perforation, accuracy, and shrinkage without intricate, optical, and mechanical equipment, and the incidental loss of time and money. This rule (Fig. 1) consists of a light metal bar having two pins at the left end and a groove 35 mm. in width for its entire length. The film to be measured is fastened over the pins, depressed into the groove and pulled tightly against the pins to the right over the end of the rule, as shown in Fig. 2. Underneath, where the film perforations rest, are square black marks, 2X3 mm., printed on the ruler. FIG. 2. The rule with film to be measured. The distance between these squares is slightly greater than the standard distance between perforation holes on new film. For this reason, these marks shift as regards the area seen through the perforation holes until the difference finally amounts to the width of one perforation, or 2 mm. It is easy to recognize the point at which the