BOAC - its a quite a few years ago now so the memory may be a bit hazy but we filled the wing tanks till the valves shut off - the gauges totalled 9,300 kg but when I dripped the tanks we had 9,100 kgs - now I cannot recall what the calibration is on the dripsticks, so maybe if its kgs that assumes a certain sg?
Agree the best way is calculate the required uplift based on actual sg and pump it in and then do a gross error check.