Mizter T wrote:

Nobody making a through PAYG journey who is merely interchanging at
Farringdon need touch on the validator, but the design of the system
sensibly assumes that people will even if they don't need to and so is
designed to tolerate this. And, as I said earlier, in some cases in
the near future passengers may specifically be requested to touch on
such a validator within a paid-area so as to prove they went one way
rather than another, thus enabling them to take advantage of the
cheaper (i.e. non-zone 1) fare.

Prediction. Just after they announce that, someone will come along here and
complain that it isn't on, because his movements are now being tracked more
accurately by 'big brother' TfL...

Paul S