"Gareth Davis" said...

While this is easy with the fixed station
readers it is far more difficult to do with the bus ticket machines,
or the hand held terminals in use on the DLR or by the RPIs -
especially given they are often underground well out of range of the
GSM networks. I would expect (although I'm only guessing since I don't
work for LT or Cubic) that the mobile readers will store details of
all transactions then offload them to the central database when they
are docked at the end of each working day. Hence working it all out
retrospectivly is much easier (and likely to be more accurate) than
working in real time.

So, is it possible to retrospectively work out capping details after the end
of each working day, and then refund the difference back into each Oyster's
prepay account if needed?