On 3 Jan, 20:19, "Michael R N Dolbear" wrote:
martin wrote
* * * * [...]
It just happened that my wanderings yesterday took me on some buses -
the first two were charged at 1.20, then the third was 95p - meaning
that I'd been capped at the z2-6 off-peak Railcard cap of 3.35,
rather than the 3.90 adult bus & tram cap.
* * * * [...]

I think what is going on here is a system rule which is nowhere stated.

"No backwards causation" perhaps *or "no subtraction"

ie, capping must work so you aren't charged more for a different order
of journeys and thus an additional journey can't reduce the cost.

In the current case if you journey on U'ground or O'ground z2-6 before
reaching the cap (which is the smallest railcard cap) then you must be
capped at 3.35. If "rail & tram only" means a higher cap then a
U'ground or O'ground journey /after/ going above 3.35 will require a
negative fare to be charged to get the same result !

And your observations causes me to wonder if things are different if
the bus journeys were before 09:30.

For a similar case, see a supermarket offer of "buy three and the
cheapest is free". *The discount should be given at the very end to
avoid the result depending on the order in which items are scanned if
you buy more than three.

--
Mike D

think you meant to type "bus & tram only" rather than "rail & tram
only"

Mike is correct - the system is programmed so that you after every
bus / tram entry and every Tube/DLR/NR exit, the payg total for the
day can never be less than the previous running total.

So - Oyster card with National Railcard discount loaded - Off-Peak
bus / tram travel only - will cap at the 2-6 discounted cap.

The info online is misleading.