On Mon, 31 Oct 2005 21:54:49 GMT, David Howdon
wrote:

For instance if I were travelling from Wembley Park (zone 4) to Sudbury
Hill (zone 4) via Rayners Lane (zone 5) and had a zones 1-4 card would I
need to touch my Oyster to something at Rayners lane.

No.

AFAIK, the system looks up in a big table that tells it that a journey
from Wembley Park to Sudbury Hill involves travelling through zones 4
and 5. It would charge the single zone extension fare appropriately.
(In fact, even if you went via zone 1 and didn't pass through zone 5,
it would still charge you the extension for the same zones 4 & 5
journey.)