DIALING HABITS OF TELEPHONE CUSTOMERS 47 



most applications after reviewing the above Sterling-3 results and other 

 line finder data collected in step-by-step offices. 



MEASUREMENT OF THE j FACTOR BY CLASSES OF SERVICE 



As indicated pi-eviously, the data recorded on the tapes showed the 

 states of being bus}^ or idle and of changes in these states for line finders 

 and the associated trip circuits. A fully equipped line finder group of 

 400 lines has ten trip circuits each of which serves two sub-groups of 

 twenty subscriber lines in the following manner. When a line originates 

 a call its line relay is operated. This causes a ground to appear on a 

 lead which is common to all twenty line relays in the sub-group and 

 starts a line finder hunting for the calling subscriber's line. As soon as 

 this hunt is completed the cutoff relay associated with the calling Une 

 operates and disconnects the line relay, removing the ground (unless, 

 of course, another line in the sub-group has originated a call in the 

 meantime). During periods of overload when line finders are not im- 

 mediately available, the ground due to a single subscriber will persist 

 until : 



1. A line finder is obtained, or 



2. The subscriber abandons the attempt, or 



3. The subscriber receives an incoming call which operates the cut- 

 off relay. 



The twenty leads from the trip circuit sub-groups were brought out 

 to the pen recorder and a record taken of the grounds that occurred on 

 each lead. Except for the possibility that more than one subscriber is 

 waiting for service at the same time on a given trip circuit sub-group, 

 the record of the occurrences of the grounds gives a substantially ac- 

 curate'^ record of the demands for service and of the number of calls 

 waiting for service. Hence- an analysis of the events occurring on the 

 trip circuit sub-groups and on the line finders as recorded on the tapes 

 gives a means for determining H. The quantity H was introduced in 

 equation (2) in the term 



^"""^^""V C^ + 1) (18) 



For convenience in the ensuing discussion this term will be replaced by 



' To obtain absolute accuracy would require the use of a pen recorder with one 

 pen for each of the 400 subscribers served on a line finder group plus one for each 

 line finder. 



