Wait Till He Sees a Cell Phone

I was waiting in line this morning as a gas station cashier explained the customer discount program.

Cashier: You see, you swipe this card, and it keeps track of your purchases. When you reach $50, you get a discount.
Man: I understand THAT part. But how does this card work?
Cashier: You swipe it, like a credit card.
Man: But how does it know what I'm buying?
Cashier: It tracks your purchase. When you swipe the magnetic stripe.
Man: What is it? What tracks my purchase?
Cashier: The system that the cards are connected to.
Man: But how? HOW does it know? How can it possibly KNOW that?

At this time, I decided a) to purchase coffee elsewhere, and b) to first check the parking lot for the pile of discarded colonial garb this man shed when he was transported from the mists of the past. I really need a new tricorn hat.