The first 3 digits indicate the Passenger Reservation System (PRS) via which the ticket is purchased.
In terms of the train 's beginning station, the first digit is determined by the train'
s zone.
Zonal Codes - 1(SCR Secunderabad PRS);2,
3(NR, NCR, NWR, NER New Delhi PRS);4,
5(SR, SWR, SCR Chennai PRS);6,
7(NFR, ECR, ER, ECoR, SER, SECR Calcutta PRS);8,
9(CR, WCR, WR Mumbai PRS) The last seven digits are generated using a random method.These digits don't have anything to do with the ticket or the travel. They only provide the PNR number a distinctive identification.