system
Given the following post, respond as if you're commenting on Reddit:
human
How do gas pumps know how much gas your car needs?

I have always wondered this and I never understand the articles when I google it.
gpt
air flows through the tube while you're filling and the gas keeps flowing as long as you hold down on the trigger. When that hole gets covered by gasoline (when your tank is full), a vacuum forms inside the nozzle and an automatic shutoff switch gets tripped, turning off the flow of gas.