Either way, the operator would simply break into the line and determine if it was 'off the hook' or 'engaged'. Have done that, the operator in this case realised that as there was no conversation in progress, and therefore determined the phone was 'off the hook'
Some parts of previous exchanges/posts
You are posting crap. The Chelmsford Telephone exchange was one of the most modern in the UK. Operators had lights and sounds to assist. I have set all this out many times. Either you did not read my posts or you have memory issues.
You are still wrong. The operator could cut in but she did not need to do this. The switchboard indicated the line status.
Yes, a telephone operator can typically tell the difference between a phone that is off the hook and one that is engaged. When the operator plugged in the signal received gave the answer.
When a phone is off the hook, it usually results in a continuous tone or a “howler” tone after a certain period, indicating that the receiver hasn’t been replaced properly. On the other hand, an engaged line will produce a busy signal, indicating that the line is currently in use.
That is how JR knew it was off the hook. The tone heard gave the answer. In this case she would have heard the howler and nothing else since the howler had been automatic since 1959.
The Chelmsford telephone exchange system was one of the first digital systems in the country. Telephonists could tell the status of a line by both lights and sounds. If off the hook was registered there would be a yellow light and the sound called the howler would be heard by any telephonist who accessed the line.
The engaged tone was a repeating double bleep. Two 400 Hz bleeps. The engaged light was red and the idle light was green. Satisfied?