This episode demonstrates how a call was traced through an old mechanical switching system. The technician literally had to trace the wires through each switch (1 for each digit of the phone number) to find the line it came in on. This is why the caller had to stay on the line for 5 to 10 minutes for the call to be traced. Success depended on a very skilled technician to complete the trace quickly. With a modern digital switch, everything is run by computer. The computer has to decode the dialed number so that it 'knows' who is calling and who is being called even before the phone rings.