TANDEM OPERATION IN THE BELL SYSTEM 



385 



with respect to manual offices to which direct trunks can be justified, is 

 to display the number dialed by the customer on a call indicator located 

 on a "B" position in the manual office, the operator at this position 

 completing the connection to the called subscriber's line. Where 

 direct trunks cannot be justified, the call indicator may be located on a 

 manual straightforward tandem position, thus forming a "call indicator 

 tandem." The operation at the tandem board is dissimilar in the 



Fig. 2 — Detroit manual straightforward tandem switchboard. 



following respects to the manual straightforward tandem operation 

 described above: a) the display of the central office code and digits 

 of the called number, as dialed by the subscriber, take the place of 

 the name of the central office desired passed orally by an operator; 

 h) the tandem operator passes the order orally to the called office; 

 c) the tandem operator is not connected automatically to the incoming 

 trunk but, upon receiving a signal on a trunk indicating an incoming 

 call, depresses a display key which connects her telephone circuit to 

 the trunk and causes the number which has been dialed to be dis- 

 played on the call indicator. 



The call indicator tandem arrangement is shown schematically in 

 Fig. 1, and a photograph of a typical call indicator tandem position is 

 shown in Fig. 4. 



