358 BELL SYSTEM TECHNICAL JOURNAL 



diately afterward the mechanical apparatus, through interconnection 

 of the tape sender and other relay circuits, proceeds to type out on 

 the page printer a summary of the test results, which may also be seen 

 in Fig. 3, in the fifth line. 



This line of the record may be translated as follows: The list num- 

 ber is 450. The circuit condition is B. The next number, 18, indi- 

 cates the number of lists which have been called since the beginning 

 of the group of tests. Observer No. 1 made 50 errors, observer No. 2 

 also made 50 errors. No. 3 made 60 and No. 4 made 46. The trans- 

 mitters used at each end are identified by the entry T3. The average 

 magnitude of the noise at the receiver terminals was 46.0 db; that of 

 the speech was 70.1 db, in each case above an arbitrary reference value. 

 The initials of the caller are added afterwards in ink. The printed 

 data in the next 5 lines refer to the comparison circuit over which the 

 same caller immediately called the next list, which for convenience is 

 on the same strip of perforated tape. 



Some specific figures concerning the advantages of mechanical analy- 

 sis may be of interest. When the observers make written records 

 which the crew itself analyzes, a usual rate of testing (using eight 

 callers and four observers) is about one comparison of two circuit 

 conditions per day. This rate can be greatly exceeded in a short 

 series covering a few conditions, but for long programs of tests in- 

 volving many variable factors this is a representative figure. Using 

 mechanical analysis, the rate of testing can easily be made to cover 

 two such comparisons a day. This includes a liberal allowance for 

 time used in circuit maintenance and clerical work. Mechanical 

 analysis, then, permits, in a given number of weeks, a program with 

 at least twice the number of test conditions ; or, a more usual disposi- 

 tion of this time, the entire program can be repeated at least once in 

 the same number of weeks, and the tests on the basic circuit conditions 

 several times. 



It is also interesting to note that the use of the mechanical recording 

 system has had several beneficial effects on the members of the testing 

 crew. Not only do they find the work less fatiguing than when written 

 records were used but their ability to see the results of their observa- 

 tions immediately after the calling of a list has noticeably increased 

 their interest in doing a good job. 



Apparatus for Control and Analysis 

 The Control Board 

 A control board, which is shown at the left in Fig. 4, permits the 

 engineer in charge easily and quickly to supervise the testing. By a 



