system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 how does the restaurant get the tip from my card when they have already swiped it?

I'll get the bill, hand them my card, and they'll bring me back the receipt where I write down the tip amount. At this point I take my card and go.  How do they get the tip off the card?
gpt
They don't actually charge your card until the end of the night.  When they swipe it they're just getting the information off of it and checking that it's valid.  Later somebody goes through the signed slips, adds the tips, and runs the charges.