Roland Perry wrote:
In message , M J Forbes
writes
Where does an westbound Heathrow train become eastbound? T4 ot T123?

It's been said in here several times that T123 is the timetabling
point. However when I was on one such train recently I noticed that
the displays inside the carriage changed to "Cockfosters" at T4.

Presumably for the benefit of people boarding at T123? Drivers have long
been changing the destination blind at the penultimate station, both to
advise those joining the train at the terminal and to save a minute or two
allowing for a pee or a can of tea.