In article , Gareth
Davis writes
For example if only the last 10 journeys are held and the period is 24
hours then a two zone tube journey could be made on peak (£2 prepay),
followed by 10 bus journeys (that would be capped at £2.50 for a one
day bus pass), followed by another £2 tube journey. The bus journeys
would have 'pushed off' the first tube journey resulting in a £6.50
total for the day rather than a £5.30 day travelcard because the first
journey can no longer be 'seen' by the program in the gate responsible
for the capping. While I admit this is a very contrived example it
illustrates the problem well

And the answer is obvious - don't program it that way. Instead, keep a
sufficient state to allow you to deduce what possibilities could come
up. So, for example, the pass slots can hold entries on the amount of
bus and rail fare paid that day. If I modify your example slightly, and
start with a completely blank card, the sequence would be:

Passes Last 10 journeys
1.00 0.00 Bus
1.00 2.00 Bus, Rail
2.00 2.00 Bus, Rail, Bus
BusP 2.00 Bus, Bus, Rail, Bus
BusP 2.00 Bus, Bus, Bus, Rail, Bus
BusP 2.00 Bus, Bus, Bus, Bus, Rail, Bus
BusP 2.00 Bus, Bus, Bus, Bus, Bus, Rail, Bus
BusP 2.00 Bus, Bus, Bus, Bus, Bus, Bus, Rail, Bus
BusP 2.00 Bus, Bus, Bus, Bus, Bus, Bus, Bus, Rail, Bus
BusP 2.00 Bus, Bus, Bus, Bus, Bus, Bus, Bus, Bus, Rail, Bus
BusP 2.00 Bus, Bus, Bus, Bus, Bus, Bus, Bus, Bus, Bus, Rail
BusP 2.00 Bus, Bus, Bus, Bus, Bus, Bus, Bus, Bus, Bus, Bus
T/card Rail, Bus, Bus, Bus, Bus, Bus, Bus, Bus, Bus, Bus

- especially if the capping period is
scaled up substantially (to say, 1 week) without increasing the
journey storage capacity on the cards.

Same solution.

And once you increase the
amount stored on the card it takes longer to read and write back -

And doing it this was doesn't affect the amount to be transmitted (in
particular, you don't need to send the list of previous journeys).

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Clive D.W. Feather | Home:
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