[PaulM]

This looks like it should have been a patentable idea but (so far) I can find no patent relating to the technique. Nothing for L E Weaver, or the BBC or even anybody else. Patent searching is obviously a tricky thing because an idea like this can be buried as IP inside something completely unrelated.

The BBC does love the sound of its own trumpet, so it's odd that if it was truly a BBC idea/invention, why this was not picked up and run with in the normal way of the Corporation.

The answer may be that the idea came from elsewhere, possibly some other field such as radar (brightness was sometimes used to show received signal strength), or perhaps telerecording, where a CRT needs is filmed and the black would have to be set accurately. Any other ideas?

Just a thought or two there - but no record of the IP as a patent seems strange.

Best regards,

Paul M