DIALING HABITS OF TELEPHONE CUSTOMERS 



45 



of load carried, it may be noted that most of the theoretical dial tone 

 tester delay curves are in close agreement with the observed data, with 

 a tendency perhaps to be slightly high. On Figs. 1(b), 1(d), 2(b), and 

 2(d), which are for dial tone delays greater than ten seconds, it may be 

 noted that the theoretical curves have a slightly stronger tendency to 

 lie on the high side of the observed data. On Figs. 3 to 6 the theoretical 

 dial tone tester delay, curves A, again lie in the proximity of the curves 

 of the observed data, with a tendency to lie higher than these latter 

 curves, especially at the ends where the dial tone delays are greatest. 

 Among the factors which account for this discrepancy are: 



1. A feature is present in panel line finder circuits for momentarily 

 releasing trip circuits with waiting calls to prevent the orphaning of 

 calls under certain trouble conditions. The release occurs after a call 

 has been waiting from 5 to 12 seconds and reoccurs every 7 seconds 

 thereafter. When such a release occurs the call yields whatever Avaiting 

 preference it may have had to a subsequently placed call which is not 

 5^et affected by such a release. The dial tone test calls did not wait 

 beyond 12 seconds. Hence for these test calls there was only one possi- 

 bility of such a release and for many of them the release occurred near 

 the end of their waiting period. Hence they were more likely to gain 

 preference over other calls than to lose their preference. 



2. Subscribers while waiting for dial tone frequently become impatient 

 and proceed to flash (move their switchhook up and down). While 

 flashing, a subscriber may lose preference to a subsequently placed test 

 call (the latter of course does not flash). 



3. Many subscribers fail to observe dial tone and proceed to dial. 

 During such dialing, a subscriber may lose preference to a subsequently 

 placed test call. 



4. Line finders serve a large proportion of call attempts of short 

 holding time whose presence may militate against the occurrence of 

 the longer delays. In connection with the measurement of the j factor, 

 the following proportions of call attempts and average holding times 

 were noted on which no dialing occurred or where no more than two 

 digits were dialed. 



Partly estimated 



