wrote:

"Finished your journey? Touch the purple validator to ensure you
are charged the correct fare".

Or perhaps more logical one to signify that you are continuing it.

Even better, just close the journey if a touch-back-in doesn't occur within
the OSI time period, if necessary the next time the card is used. Don't
see why that's hard.

Neil
--
Neil Williams in Milton Keynes, UK. Put first name before the at to reply.