In article ,
Mizter T wrote:
My guess is that it is just a single bit on the Oyster card, so one
size must indeed fit all. *Or actually two sizes, namely auto top-up
enabled, or auto top-up disabled.

Well, auto top-up by £20, or auto top-up by £40.

Yeah, I realised that after I posted. So there are three states (off,
20 quid or 40 quid). If we assume there must therefore be at least
two bits coding the state, that means that it would be possible to
support at least four states.

-roy