How do Cessna 152 fuel gauges work? I can't remember - do they have a float and a thermal gauge like a car? If so they are very crude and prone to misreading and malfunction, especially on an old aircraft.
Modern airliners have multiple point capacitance fuel level measuring devices in each tank - all of which have to agree with other to give a reading on the fuel gauge. We also calculate how many litres we will need to load the fuel we want, and we cross check that with the literage delivered by the fuel bowser. If the actual figure is more than 5% different to the calculated figure, we have to "dip" the tanks and find out where the discrepancy is.
One of the most fundamental things to get right in aviation is to be absolutely sure that the fuel you need for your flight is present and on-board in the tanks. Getting this wrong is potentially life threatening, so should never be assumed or treated lightly.
If you run out of fuel in an aircraft, you can't pull over to the side of the road and call the AA..........
The Cessnas I flew back in the day all had a wooden dip stick in the shape of a T that we used to double check the fuel level in the tanks.
@tourist: even if you have perfect fuel measuring systems, you should always double check something as fundamental as the amount of fuel on board.
