When the gas/petrol tank (in the car) reaches full level,there is a mechanism to trigger off the pump latch and at the same time a return-valve is opened (at the top of the pump station) to allow excess gas/petrolto flow back into the sump.
But the return gas/petrol has already passed through the meter, meaning you are donating the gas/petrol back to SHELL/CALTEX/MOBIL/ PETRONAS
Warmie
