It must have been a common thing with Econet Bridges to scribble all over the front of them with the numbers of the two network segments the Bridge was connecting. Here, they are network 1 and network 3.

Perhaps the people who were doing this were quite forgetful, or weren't aware that the Bridge can be interrogated using the WHATNET call to establish what network number it is connected to, or the ISNET call to determine whether a given network number can be seen by the Bridge.

The Bridge itself stores the numbers of the two networks and allows communication between them provided that the network numbers are specified by the user stations.

To log on to file server Station 254 on network 3 from network 1 you would need to type *I AM 3.254 USER. The local network number is zero, and it is not normally necessary to specify this when referring to a station on the local network, but it is essential if previously the user station has been communicating with another network across a bridge. To log on to the local network having previously being using station 3.254, it would be necessary to type *I AM 0.254 USER to communicate with the local network Station 254.