F. H. Richardson's bluebook of projection (1942)

270 RICHARDSON'S BLVEBOOK OF PROJECTION tion and repaired or replaced at the slightest sign of imperfection. No conscientious projectionist, unless he were compelled by conditions or an indifferent manager, would use crooked or damaged reels, risking injury to prints. It is wise to stamp all theatre reels with the name of the theatre and to guard against sending them to the exchange by mistake. How to Estimate Footage in a Film Roll (61) How may the footage in a roll of film be estimated ? Because film varies between 55/10,000 and 60/10,000 of an inch in thickness and because the tightness of the winding varies in different rolls of film, it is possible to calculate the footage contained in any roll with only approximate accuracy. However, it may be estimated as follows, using inches for all measurements: (62) First add the circumference of the opening (reel hub) in the center to the outer circumference of the film roll. Divide by 2. This will give the average length, in inches, of layers of film in the roll. Next, measure from outer to inner diameter of the film roll and divide by 5^4 (a compromise between the film thickness of 55/10,000 and 60/10,000 of an inch). Result will be the approximate number of layers of film in the roll. Multiply this by the average length of the layers and divide by 12 to get the number of feet. Final results will be footage of film in the roll as nearly as it can be arrived at by computation. Measuring Film Accurately (63) To measure the length of a reel of film accurately count the rotations of the projector mechanism crank shaft. Exactly one foot of film is passed with each rotation. Film measuring devices may be purchased from supply dealers. Removal of Emulsion (64) To remove the emulsion from the film, first soak it in a bucket of warm water to which has been