On Sat, 16 Sep 2006 23:31:49 +0100, Barry Salter wrote:

It's also worth noting that there are Oyster validators on the Central
Line platforms at Stratford (or at least there were last time I went
through), so you might want to touch in there as well, just to be on the
safe side.

It's my understanding that (when using PAYG) you generally only ever
need to touch twice on each journey - once when you start your PAYG
journey and once when you finish it.

The exception to this is when using an out-of-station interchange at
some point during your journey, such as at King's Cross or
Hammersmith, in which case you'll also need to touch when leaving and
re-entering the Compulsory Ticket Area, making four touches in total
(or 6 if you make two OOSIs during a journey, etc).

Also, London Bridge (Thameslink) and Wimbledon may be special
exceptions.

I'd better add a disclaimer that this contradicts some TfL advice,
which advises you to make extra touches at stations like Bank and
Farringdon (not to mention the fact that most standalone validators
have a sign telling all passing PAYG users to touch there). However,
making these extra touches shouldn't, in theory, result in you being
charged any more for your journey.

Whew, that post (like most Oyster ones) ended up a bit longer than I
expected...