DIALING HABITS OF TELEPHONE CUSTOMERS 33 



ized trunking formula's "j" factor describing the degree to which cus- 

 tomers wait when dial tone is not immediate.'- 



3. Comparisons of observed and theoretical distributions of the num- 

 bers of simultaneous calls on the line finder groups. 



4. Statistical accounts of the actions of subscribers when dial tone 

 is delayed. 



GENERAL PLAN OF THE TESTS 



The general plan of the tests was developed around two specially- 

 constructed devices : 



1. A 100-pen recorder capable of recording observations continuously 

 for two hours and sensitive enough to record individual dial pulses. 



2. A speed of dial tone measuring set comprising a means for manu- 

 ally originating test calls, and an electric timer which automatically 

 stopped when dial tone was received. 



Tests were conducted on a weekly schedule, one or two line finder 

 groups being studied each week. Two 100-pen recorder tapes were run 

 daily. The first was run from 10 A.M. to noon for message rate individ- 

 ual, fiat rate indi^'idual and message rate two-party classes of service to 

 include the morning bus}^ periods for these customers. For coin customers 

 the first tape was run for two hours during the noon coin busy period. 

 The second tape was run in the afternoon from 2 to 4 P.M. for all 

 classes of service except coin. For the coin class the second tape was run 

 for two hours during the early evening coin busy period. Three message 

 rate two-party tapes were run in the early evening busy period, and two 

 coin tapes were run in the afternoons when World Series baseball games 

 were being played in Brooklyn. A summary of the number of line finder 

 groups observed, the number of tapes taken, the number of line finders 

 made a^'ailable and the maximum per cent dial tone delays over three 

 seconds are given in Table I. 



Except for the morning runs on the message rate individual line 

 groups where an effort was made to maintain a fixed number of twenty 

 line finders throughout, the number of line finders made available was 

 selected by close observation of the flow of traffic. All studies were by 

 half hours during -w^hich the number of line finders was held constant 

 as far as possible. At the end of a half-hour period the number of line 



2 This formula for both finite and infinite sources was developed by R. I. Wil- 

 kinson in 1930, and appeared in the 19.36 Bell Telephone Laboratories Out-of-Mour 

 Course "The Theory of Probability as Applied to Telephone Trunking Prob- 

 lems." This formula for infinite sources was also developed by Conny Palm and 

 appeared in "Etude des delais d'attente" in Erickson Technics — No. 2 — 1937. 



