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lamp, to which the outgoing signals are also supplied. In order to see 

 this monitoring lamp from the operator's position, a right-angle prism 

 and a magnifying lens are placed in front of the disc and the image is 

 observed through an opening in the side of the motor cabinet. The 



Fig. 14 — Sending and receiving discs, with neon lamps and optical arrangements 



for image monitoring. 



task of the operator is to direct the scanning beam up or down by 

 means of the variable angle prism until the face of the person in the 

 booth is centrally located. This adjustment is facilitated by a wire 



