peter wrote:
Not sure how useful it would be on the web, even if they did work!

But at the stations .... Those on the Piccadilly are totally
unreliable - not only the time, but also the final destination is often
wrong. This matters when you are going to a station beyond Arnos Grove.

It is quite useful on the web actually.
I can check the Northern Line arrivals at Bank before leaving the
office, and get a good idea of what state the line's in by the headways
between trains.