In message ,
Colin Rosenstiel writes
Again as mentioned elsewhere in the thread, the whole of the back of
the ticket was a magnetic surface. However these tickets were much
smaller than the current tube tickets.

Same size as a 'proper' Edmondson ticket IIRC

No, longer than an Edmondson, I'm sure. I have examples somewhere here.

On thinner card, too. Somewhere I've got one that was issued by a
pre-deployment demonstration system they installed at the Science
Museum. I think Clive might have one of those, too.
--
Roland Perry