Paul Corfield,

Many thanks for the explanation.

As a lawyer, used to some pretty complicated concepts, I still find the
whole Oyster thing mind-boggling, and the more I learn about it (to say
nothing of having to explain to some jobsworth where I got on and where
I am going to, should the reader have failed to register my Oyster, and
the traceability of my journey, which is nobody's business but mine)
the less I want to have to do with it. I'll still be buying One Day
Travelcards at my corner shop for the foreseeable future. Much simpler
all round - and simple proof of payment for the taxman.

Marc.