INTERTOLL TRUNK NET LOSS MAINTENANCE 965 



Statistical analyses must thus be made of data for small groups as 

 well as for large groups of trunks. Furthermore, the groups which arc 

 studied must have elements or factors in common in order for the statis- 

 tics to have significance. Analyses of periodic measurements of losses for 

 the same trunk or groups of similar trunks can likewise indicate signifi- 

 cant changes in performance. 



As yet, the problems of properly selecting the trunks to be analyzed 

 and of correlating the results of the analyses with particular system ele- 

 ments needing maintenance attention have been solved only partially. 

 In addition to the need for proper procedures, there is the need for thor- 

 ough training of maintenance personnel. The complexity of the telephone 

 plant today is increasing the importance of all maintenance personnel 

 ha\dng a thorough knowledge of how individual systems function and 

 how the performance of the various system elements reacts upon over- 

 all trunk performance. 



Procedure for Analyzing Measurements 



In an effort to facilitate the application of statistical analysis of trunk 

 performance by plant personnel, a special data sheet and associated 

 templates have been devised. These are shown in Figs. 4, 5, and 6. The 

 method of analysis gives only approximate results but has been found 

 to be sufficiently accurate for reasonably large amounts of data. It is 

 simple, rapid and easily comprehended by the plant personnel. The 

 procedure to be followed consists first of subtracting the specified loss 

 from the measured loss for each of the trunks under study. A stroke is 

 placed on the chart for each of the resulting deviations at the intersection 

 of the appropriate classification and tally lines. For example, the first 

 deviation between —3.25 db and —3.75 db would be stroked on the 

 horizontal line for that band, just to the left of the vertical line for tally 1 

 (See Fig. 4). The second deviation in that band would be stroked just to 

 the left of the tally 2 line. This is continued until all the deviations have 

 been recorded. 



The last stroke in each j^^ db band indicates the number of deviations 

 found having values within that band. As shown on Fig. 4, for the 

 analysis by the template method this value is written in the first column, 

 marked "Line Tots. (A)." These values are added and should equal the 

 total number of measurements in the study (533 in the example). 



Next, the column "Cum. to 3^^" is filled out. Beginning at the top 

 line, totals are accumulated to the point where adding the next line total 

 will result in a value exceeding 3-^ the grand total of measurements (266 

 in the example). Similarly a value is obtained accumulating the totals 

 from the bottom. In Fig. 4 these values are 246 and 166, respectively. 



