was to decide which was the best connection to be used through the switching network, and this part was called the route choice. The interrogators would return the available paths and the route choice would make a choice and tell the markers to mark that route. The exchange used reed relays as the switching medium, and the reeds themselves were approximately 3 inches in length and the only ones available. They were provided by the Hivac subsidiary of AT&E (then the only UK manufacturer of reed inserts.) It had multi-stage switching divided into A, B and C switches, interconnected by links. A typical local call would be connected via A-B-C-Link-C-B-A. Links could each either have or not have transmission bridges for local calls. The bridges were contained within the outgoing junction units. The exchange had some advanced features for the time, including multi-frequency (MF) tone dialling as an option opposed to pulse dialling, and no post-dialling delay for own exchange calls. It also had the ability to detect a switching failure and automatically attempt a repeat dial. Any repeat attempts were logged to the teleprinter. It also had a test console, which monitored all calls on a digital edge-lit display. Another display gave a visual indication of the traffic flowing through the exchange, named the Hubblemeter after the instigator Ray Hubble. Occasionally the call trace did not work, but the engineers worked out a way of manually tracing a call. What they did was to buy a little compass and glue a piece of magnetic ferrite on the side to pull the compass needle away from north. They would then run this compass along outside of the reed relays, and when a relay was operated the needle would move back to north. This was repeated over several sets of the switching path until the trace was complete. Inter-rack cabling was via a cable loft. The cables were routed up through packed pass-throughs into a reinforced ceiling. A novel but subsequently disastrous feature designed by Bell Antwerp was used to hold the subscriber's class of service information i.e. PBX, shared service, incoming calls barred (ICB), temporary out of service (TOS) etc. This was a capacitor store, and it held information on a thin plastic strip, into which could be inserted up to 10 little copper squares which had a capacitance of 10 pF. The thin plastic strips were then inserted into