250 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



may be approximated by choosing the more economical alternative re- 

 sulting from filling in the check list given in Table IV. 



Part VII — • Summary 



In the telephone central office some 60,000 relays are needed to carry 

 out the automatic switching functions. Since the entire office is built 

 around them, they determine the cost of the office, not only by their 

 first cost, and maintenance cost, but at least equally importantly by 

 their influence on the power plant, and the amount of common control 

 equipment that is needed. There is opportunity for great economy, over- 

 all, when manufacturing cost is put in proper balance with the cost of 

 power, cost of functioning time, and similar performance variables. 



The preceding pages have shown how each factor in the total system 

 cost may be stated in a common language — the equivalent first cost 

 value. When each variable, expressed as an incremental figure denoting 

 the cost compared to an ideal standard, is so stated, all relay factors in 

 the switching system may be cross-compared. This permits a large num- 

 ber of optimizing procedures to be carried out. 



Optimizing methods for several important cases have been illustrated, 

 and relations or procedures of value to the relay designer are presented. 

 Particularly outstanding cases are the means for realizing (a) power- 

 plus-coil economy and (b) power-plus-speed economy. 



On the side of manufacturing cost, relay designers need some guidance 

 as to how their applications problems will be influenced by the lot-size, 

 or annual demand. Optimizing procedures are also given for this prob- 

 lem, to yield approximate values for optimum lot-sizes under various 

 manufacturing conditions, and the corresponding cost penalty as a func- 

 tion of annual demand. 



The steps to be taken in order to strike the best balance between 

 standardizing for maximum manufacturing economy and diversifying 

 for maximum performance economy are also given. 



The problem as a whole is a striking example of how design for service 

 can be applied on a very large scale. The economies realized by the ap- 

 proach used here have avoided the expenditure of many additional 

 thousands of dollars yearly to the telephone companies, with corre- 

 sponding economy to the customer. 



ACKNOWLEDGMENT 



Appreciation is here expressed to R. L. Peek, Jr., and Mrs. K. R. 

 Randall for helpful technical suggestions, and also to Mrs. Randall 

 for help with the preparation of figures and examples. 



