That's to validate the transaction with the bank; the station itself does not (or should not) capture that information.
I saw a TV news format show (like 20-20) several years back where the police spotted a car leaving a gas station, drive to another station, fill up, drive to another station, fill up, drive to another station, fill up, drive to another station, fill up, drive to another station, fill up, drive to another station, fill up,then finally come back into the garage for a while... then do it all over again.
Seems the station was stealing the credit card data, numbers and pins, on every card used there. The filler car was modified with a huge gas tank, they would fill it with gas paid for with OPM, dump it into the station tank, then sell the free gas at market rates.
The scary part for me was seeing blank credit cards, completely white except for the magnetic strips. Hundreds of them in the back room.
