ECONOMICS OF TELEPHONE RELAY APPLICATIONS 



235 



the equipment restores to normal, ready to serve the next call. It takes 

 a. marker about a half-second to do its job; nevertheless many markers 

 may be needed to handle the traffic during each day's heaviest calling 

 period. Since the cost of each marker is measured in the tens of thousands 

 of dollars, it becomes a matter of great importance to shorten the marker 

 work time — in other words, to shorten the time of each relay in the 

 chain of marker events. Since faster relays are usually more expensive 

 it is important to find the dollar value of speed so as to guide an intelli- 

 gent design of each speed relay. 



As in the case of power, it has been found possible to state the value 

 of speed in terms equivalent to the manufacturing costs of relays. This 

 may be done through a knowledge of the number of markers and asso- 

 ciated equipment needed in relation to their work time, and their cost. 

 Such relationships are shown in Fig. 7, which gives a typical curve for 

 the markers per line needed to handle the traffic. Then, when the value 

 of the marker is known, the value per line per millisecond, Ct , follows. 

 Corresponding to this, a value per millisecond per marker, Cm , can then 

 be found, which varies inversely as the number of markers needed : 



_ ^' 

 Cm — — , 



V 

 where p = number of markers per line that are needed. This figure is 

 the value of a millisecond for any complete event or series of events 



O 50 100 150 200 250 300 350 400 450 500 

 MARKER WORK TIME IN MILLISECONDS 



Fig. 7 — Markers as a function of work time. 



