On 24 Nov, 18:29, David Cantrell wrote:
There's no real fix for this,
other than them SMSing me as soon as possible after every transaction
with my current pre-pay balance, or something of that ilk.

You should be able to check the cost as you go on the screens on
readers. Every gate and standalone reader has a screen that shows you
your balance and the amount being deducted. There seems to be two
types of gates - one shows the numbers on the post next to the gate
(where the green arrow lights up) on both entry and exit. The other
has an LCD as part of the Oyster pad, but only on the pad you use when
exiting, meaning you don't get shown your balance on the way in on
this type.

U