Apologies Swedish Steve, it's been a long week.
Most airlines don't trust the A/C Fuel system due to accidents/incidents (ran out of fuel) and tail scrapes etc. Due to errors.
So.
Most airlines take the fuel figure from the bowser in Liters / Gallons or Imperial gallons and using a correction plus the SG provided by your good self convert it to KG or pounds depending on if your aircraft has a metric system or imperial, some operators have both systems as they buy lease A/C from different states. As I'm sure you know.
We then cross check in my case the KG loaded plus the previous fuel on board and confirm it totals within limits (usually less than 1000KG) with what the A/C tells us. As stated above any discrepancy investigated ie a two step fueling with APU burning a few hundred KG might be a source of error.
Now I've just confirmed that our company uses standard SG of 0.78/.80/.82 to construct the load sheet weight and balance dependent on location on the planet and season to try and closely match what will be the actual SG.
This way the data provided should mean the aircraft behaves as expected
Now I just asked the refueler today what he does and the interesting thing is and I'm not sure if this is standard but he said if I order 90,000 KG not be loaded but to be the fuel onboard after fueling is complete and say we have 10,000KG onboard already and his SG is 0.8 he converts that to liters and dials up 100,000 liters on the truck and pushes the go button.
So when it boils down to it, it's a bit redundant that he converts weight into liters and we convert liters back into weight. All we've done is check our button pushing abilities.
I think we all just assumed they push the go button till the A/C says 90,000KGs and then the refueler read off the liters that went through the truck.