234 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



uring devices, such as the artificial mouth, artificial ear, with calibrated 

 condenser transmitters and oscilloscopes, are carried to the factory assembly 

 line to measure precisely each instrument as produced. 



In the case of the instruments of the 1950 set, knowing that they were 

 destined for large scale production by modern machines, tools, processes 

 and assembly lines, the design for production was carried along with the 

 design for performance. Thus the dictates of theory and laboratory per- 

 formance were being continuously matched with those of fabrication and cost. 



Design for Service 



It has long been the practice in the Bell System to make trials in the 

 operating plant of laboratory models or samples from the initial production 

 of new designs. This has two major purposes — one to determine functioning 

 under service conditions and the other to detect if there are weaknesses 

 which may result in unexpected deterioration or failure. In addition, routine 

 and special studies are made of service performance and troubles through- 

 out the use of a device or system. As a result, information is continually 

 being supplied to the designers to show the benefits of improvements and 

 the needs for changes. This knowledge of service functioning and main- 

 tenance can thus be coordinated with the procedures which have been 

 termed "design for performance" and "design for production." In the de 

 velopment of new designs or the modification of current ones, the Bell Tele- 

 phone Laboratories designer is in a position to integrate concurrently the 

 dictates not only of the laboratory and of the factory, but also those of 

 service performance. This "design for service" can be carried out in the 

 interest of getting the optimum ratio of service for the users, to the cost of 

 employing the device in the plant, including not only the carrying charges 

 on the initial price but also the cost of its operation and maintenance. Since 

 the customers of the telephone system are paying for service and not buy 

 ing equipment, the purpose of "design for service" is directed toward the 

 goal of giving the most service for the money. 



One result of this integration of plant experience into design has been a 

 reduction in the last fifteen years of four to one in the service troubles with 

 telephone instruments in the Bell System plant. These devices now approach 

 the performance in this respect of many passive circuit elements. 



Conclusion 



In closing this scant presentation of the scope and results of the ac- 

 tivities which have been carried on in Bell Telephone Laboratories primarily 

 to improve the telephone devices invented by Alexander Graham Bell, men- 

 tion should be made of the many important benefits which have been de- 



