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663 HANDBOOK OF PROJECTION FOR
itself, is in movement, and to subtract that number of degrees from 360 to know the exact ratio of movement to rest.
If, however, we place marks A and B directly on the wheel itself, it will be difficult to measure the number of degrees between them accurately, hence we suggest the following plan.
There are two methods for taking the record, either one of which is excellent, but the first, while the best, in that no protractor is necessary for the final measurement, is difficult of application on the Simplex, because of the proximity of the face of the flywheel and mechanism casing.
Cut a strip of paper about half an inch wide and long enough to go around the circumference of the flywheel, with half an inch to spare. Place this strip around the face of the wheel, put a dab of paste on the overlapping end and press it down, holding it until it sets and holds the paper band in place.
Now, proceeding as before set forth, locate points A and B, figure 230b, placing the marks on the paper .instead of on the wheel, though it might be well to add the marks on the wheel also, since you then will have a permanent record on the wheel itself.
Having made the marks on the paper band, draw a sharp knife blade across, exactly at one of the marks — either one — severing the paper, whereupon you will have a strip of paper, on which is a mark, much nearer one end than the other. The short end represents the movement of the intermittent sprocket; the long end its period of rest.
You may now transpose these two distances into ratios of movement to rest by either one of two or three methods, one of which is as follows : First, measure the exact total length of the paper, in inches. Multiply this by 1,000 to reduce the measurement to thousandths of an inch. Divide this result by 360, the number of degrees in a circle, and you have, as a result, the width of one degree of a circle the diameter of your flywheel, in thousandths of an inch.
Next measure the exact length of the shorter distance of the mark from the end of the paper and multiply this result by 1,000 to reduce it to thousandths of an inch, whereupon you have only to divide this last result by the width of one degree, in thousandths of an inch, to ascertain the number of degrees during which the film moves in your projector, and the subtraction of the final result from 360 will give you the period of rest, in degrees, as well. We would, however, suggest the advisability of also reducing the longer end of the paper to degrees, so that by adding the two together you