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MANAGERS AND PROJECTIONISTS 662
edge of the face of the flywheel has moved while the intermittent sprocket is in motion, we will then have the number of degrees that edge has moved while the sprocket is moving, and since there are 360 degrees in the complete circle, that number of degrees subtracted from the total of 360 gives us the number of degrees the intermittent sprocket is at rest, and by comparing the two we have the ratio of the time the intermittent sprocke is in movement to the time it is at rest.
TO MEASURE THE RATIO.— In order to measure the ratio of movement, we first must haVe a locating mark on some stationary object, such as the projector mechanism frame, right close to the edge of the rim of the flywheel, and since this is not possible with all projectors, I would suggest the attaching of a board or block of wood to the side of the mechanism table, by wiring or any other convenient method which will insure its immovability.
In the side or top of this board, or block of wood, bore a hole just large enough to permit of a stiff piece of wire of suitable length, filed to a sharp point at one end, being driven into it tightly. To do this grasp the wire firmly about an inch from its blunt end with a pair of pliers, and drive the wire into the hole by hammering on the side of the pliers beside the wire.
When you have the wire firmly seated in the wood, bend it until its pointed end is as close as possible, without actual contact, to the rim, or edge of the flywheel. This is shown in the drawing, figure 230b.
Presuming the flywheel in figure 230b to move in the direction of the arrow, and that point A of the flywheel to be exactly opposite the point of the wire when the intermittent sprocket starts to move, we make a scratch mark on the rim of the wheel. This scratch mark will, you will, of course, understand, represent the point at which the intermittent sprocket starts to move.
We now move the flywheel slowly, in the direction of the arrow, until, by means of our readjusted flat spring against the sprocket tooth, we find the exact point at which the intermittent sprocket ceases to move. We then make another scratch mark on the face of the wheel, exactly opposite the point of the wire, which is point B, figure 230b.
We now have only to measure the number of degrees between scratch marks A and B to know the number of degrees through which the intermittent sprocket, hence the film