On Wed, 2 May 2007 15:54:07 +0100, Tom Anderson
wrote:

On Tue, 1 May 2007, Paul Corfield wrote:

On Tue, 01 May 2007 18:24:50 +0100, James Farrar
wrote:

On Tue, 1 May 2007 15:05:40 +0100, Tom Anderson
wrote:

A way to do that would be for the gate to write on the ticket that it's
just been used for exit at that station, and refuse tickets that have been
so marked. This is probably actually simpler, as it avoids having to have
the gates share knowledge of which tickets they've seen.

I believe magnetic tickets hold the details of the last three uses.

No they do not. They do not have sufficient capacity to do so. If a
ticket is valid and is accepted then certain key fields are updated. It
is this revised data that allows things like passback and zig zag to be
detected.

I'm a genius!

I think we knew that already Tom. Thou art truly a man of many talents.

Hang on, what's zig-zag? I thought it was a synonym for passback, but i
guess not.

And *as* you are a genius I am sure you'll be able to work out what a
zig zag is ;-)
--
Paul C


Admits to working for London Underground!