On Wed, 11 Nov 2009 17:18:40 -0000, Paul Scott wrote:

Could someone remind me what happens if you touch in with a small
positive balance (that is less than the maximum cash fare), then touch
out following a journey that was more expensive than the balance?

You get a slight overdraft on the card.

Cheers. So it will not be until the start of the next attempted journey that
you'll find you can't touch in?

Yes. IIRC you can even do an OSI while your balance is negative
(though I haven't tried this for a while).