On 16 Dec, 14:23, Martin Krieger wrote:
For
example travelling from say South Kenton into Zone 1 via Euston you
might wish to linger a little if you arrived at Euston at 18.50 before
heading to the Tube as you'd get the cheaper price all the way through
if you re-entered after 1900.

Will it really work that way? As far as I have understood the oyster
system, the fare is calculated between the touch-in and the touch-out
point, and touches in between will be ignored. So in that particular
case, as the touch-in is before 10:00, the higher price will be charged.
The only chance to take advantage of this is to break the journey into
two separate journeys - which is not that easy as Euston is an open
interchange.


I'm a bit confused by where you've got 10:00 from, and what you mean
by Euston being an "open interchange". Nevertheless I'll attempt to
pad out the scenario that Paul was outlining...

Touch-in at South Kenton at 18:15 for the 18:21 London Overground
train to Euston. Arrive at Euston at 18:50. This part of the journey
will be charged at the 'discount' Oyster fare of £2, not the
'standard' fare of £2.50, because of the special arrangement on the
Watford - Euston line that means the cheaper fare is in force in this
direction (towards Euston) from 0930 onwards on weekdays.

Thus far, the Oyster system considers one to be on a 'discount' fare.
If the passenger then enters the LU network at Euston (or Euston
Square, as it is a valid out-of-station interchange with Euston UIVMM)
for an onward journey to somewhere else - for argument's sake let's
say it is somewhere within zones 1 to 4 - before 1900 then the Oyster
system will revert to charging them a full fare of £2.50 for the
through journey when they exit the system and finish their journey.

If however they wait around in Euston for a few minutes (perhaps
counting how many pigeons are actually inside the building) then enter
the LU network after 1900 the Oyster system will still regard them as
travelling on a 'discount' fare and will only charge them £2 when they
exit the system and finish the journey.