"John Levine" wrote in message ...

I still don't understand how that tells it which of the two valid
cards to use.

If it got an answer from both (with a suitable separation), it could
decide to use the season ticket rather than the PAYG. Doesn't have to
take just the first one, especially just after it had detected a clash.

I suppose, but that still doesn't help in the many cases where there
is no clear reason to prefer one card over another. It seems a poor
use of funds to redo the gates when it will only help sometimes.

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The gates get reprogrammed software frequently

However ISTM that the time taken to wait for the delay between the cards
re-transmitting is going to be a killer here - especially if you've three
(or four) cards

tim