Tadex,
It is my experience that fuel is not “lost” when the centre tank is empty in-flight but that the centre tank fuel will indicate up to 200kgs less in the climb due to the body angle. This returns in part when you accelerate above FL100 and all the way once you have established in the cruise. Conversely you may get some re-appearing in the descent if you did not drain the centre tank fully in the cruise. However this will disappear again at approach body angles. I have never got so low on fuel to find out if this +/-200kg is usable or not – and I hope I never do!
As regards fuel tank accuracy & compensation techniques, to quote from
my own site: “The classic fuel gauges will compensate for changes in sg and have an accuracy of ±2½%. The NG fuel quantity indicating system uses a microprocessor to analyse a capacitance signal from units in each tank. The signal contains data on fuel quality and temperature, which is then used to calculate density. The processor then sends the fuel-weight signal to the flightdeck displays and FMC with an accuracy of 1%.”
S&L