London Travel Cards, the earth's magnetic field, and british actors

Bill writes: The London 7-Day Travel Card is a nifty little card for traveling on the Underground. It's got a magnetic strip on the back and you pop it in one end of an entrance or exit gate, and it pops back out the other, and opens the gate for you to get you through the station. The problem is, the magnetic strip on the back of the card is so sensitive, that everything knocks it out of whack. The longest I've been able to use my 7-Day Travel Card is 3 days, the shortest is 9 minutes.

According to the ticket clerks I've asked about this, putting the travel card in my shirt pocket next to my cell phone scrambles the magnetic strip. So does putting it in my wallet, because of the credit cards and their magnetic strips. Even putting my wallet in one pocket and the card by itself in another doesn't work. In fact, pulling it out of it's plastic card holder creates a mild electromagnetic current that also effectively erases the card. Perhaps the earth's magnetic field is sufficient to render the card ineffective if I don't hold the card aligned with the north pole.

So the only way to use the London 7-Day Travel Card as far as I can see is to hire an out-of-work London actor (there are plenty of them around, fortunately) dressed entirely in natural fibers and have them follow me about during the day, holding the card at arm's length and pointed north until I need it. That would explain all the people I see loitering around the entrance to the Underground wearing jeans and tee shirts with their hands out--they're auditioning to be hired as Travel Card holders.