Folks,
A comment on gauge/totaliser accuracy, in part the story is covered in the changes to certification standards over the years ---- showing the development of sensible thinking over the years --- as a result of hard won and usually deadly experience.
Also the development of the concept of fixed final reserve, which is not 30m holding, but the amount of fuel, calculated or indicated, that is to take care of all the inaccuracies in fuel measurement, so that the engines are running at touchdown ---- the Boeing equivalent is minimum fuel for approach.
No gauge or totaliser system in "accurate", all measuring systems have an order of accuracy.
"Granny fuel", that I know as a "quick squirt for mum and the kids" is relatively common for small aircraft.
Airline fueling practices should be far more exacting --- including adding extra fuel when the discrepancy between calculated fuel on board, and indicated fuel on board (including having used the corrected SG--- as in correcting the average SG to account for fuel on board SG v SG of fuel loaded) exceeds 3% --- and in the case when there is a serious mismatch, drip the tanks.
And what goes on the loadsheet ---- the minimum fuel that you know you actually have on board.
Tootle pip!!