One thing led to another and the AME managed to convince the captain that the fuel onboard was actually what he had pumped in and the the totalliser was underreading!
Captain's choice, I'd say. You could also claim that the fuelling truck's gauges were overreading ... or someone entered the arrival fuel incorrectly.
However, just because there are 20 high tech ultrasonic sensors in each tank, it doesn't mean that they are infallible. If they are anything like the ultrasonic potable water level detectors on our 744ER's, the tanks could be reading full when they are empty : P
The 767 totaliser system is more accurate at certain levels, but the 777 system may have an advantage with the number of sensors in each tank. The wing being such an irregular shape, it is always difficult to calculate the volume in these tanks.
Rgds
NSEU