Cockney Steve
Will you please stop using common sense, don't you know that aircraft run on myth, old wives tails, things that bloke in the bar said....... And worst of all the thing used to explain things people don't understand.... So they call it Airmanship!
Fortunately at the big end of this business Mr Boeing agrees with you, to manually check the fuel level an an airliner they have fitted a roll and a pitch spirit levels, using the attitude information from the two spirit levels and a big set of tables you can turn the inches calibration on the sticks into an accurate fuel volume.