244 THE BELL SYSTEM TECHNICAL JOI^RNAL, JANUARY 1954 



0.15 0.2 0.3 0.4 0.5 0.6 0.8 1.0 1.5 2 3 



RATIO OF RESISTANCE TO OPTIMUM RESISTANCE, R/Rq 



Fig. 12 — Cost penalt.y when resistance is not optimum. 



Thus, the fractional change in cost caused by any departure from the 

 best resistance is readily estimated, expressed in ratio form as R/Rq . 

 This relation is shown in Fig. 12. 



SUMMARY 



In summary of Part II, methods have been given for deciding on the 

 magnet coil design which will provide the cheapest net cost in the switch- 

 ing system. When the conditions of use are known, a series of charts 

 may be prepared such as the one shown, from which the applications 

 engineer may decide the proper coil design, and how much it may be 

 worth to the system. As experience will show, the cost of departing from 

 an optimum design may run well over $1.00 per individual relay, with 

 the result that aggregate savings in the whole central office may run to 

 thousands of dollars compared to the cost when this problem is ignored. 



New relay development may be guided by the use of these same rela- 

 tions, since through a process of considering various hypothetical de- 

 signs of various sizes, work outputs and magnetic qualities, the potential 

 optimum costs may be found. Design of the recently adopted wire spring 

 relay was very materially guided by considerations of this sort. 



Part III — Choice of Contact Sets for Maximum Economy 



One of the many problems involving lot-size costs of relays is the num- 

 ber of standardized sets of contacts that should be provided: i.e., how 

 many kinds of contact arrangements give maximum economy for the 

 product as a whole? By pro\ading only a few choices of kinds of contacts, 

 for example, the annual output is less divided and there are fewer setup 

 charges, with the result that the initial manufacturing economy is large. 

 However, because of the small selection of kinds of contact sets, there 

 will result many cases where extra contacts are provided at greater than 



