Have you ever wondered how the ATM knows exactly the right amount of bills to deliver? Even though a vending machine may occasionally spit out extra crisps but an ATM machine never loses its touch. The reason why an ATM machine cannot be fooled to give more cash lies in an intricate layout of both smooth and ridged rollers, passing the bills onto a conveyor belt where they are scanned.

Skymag

Watch this video describing how an ATM machine works:

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Next time, maybe you should try your luck at the vending machine if you are hoping for something extra!