Making a manual change-over involves switches, levers and eye concentration. A switch, to turn the projector motor on and another to switch the sound, and yet another (foot switch) to change the picture from one machine to the other. Also a hand operated lever is used to move a steel plate (shield) to block the light and heat from the unused projector. Everything must happen in a precise order and at the exact time to make a seamless reel to reel movie change-over.

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