On older generation aircraft there was no automatic distribution and control system. One took the total fuel required figure given by the flight crew or dispatcher and looked up a chart that showed how much went into each tank to maintain centre of gravity and structural loads within limits. The refueller had to watch all the gauges and switch off each tank as it reached the correct figure. Only tanks being completely filled could left to shut off automatically.
There were a few cross checks employed to catch errors and monitor fuel qty system accuracy as older generation systems suffered from calibration drift and needed monitoring. Modern computerised systems are largely self monitoring and announce any faults detected.
The bowser/tanker operator always supplies a receipt in gallons or litres for the amount his meters said he had pumped into the aircraft. This figure was converted to kgs or lbs by multiplying by the SG of the dispensed fuel. This figure was then compared to the actual total indicated by the aircraft gauges by adding the indicated fuel on board before refuelling. ie. the total indicated quantity after refuelling should equal the indicated fuel before refuelling plus the bowser qty pumped in. If there was a significant discrepancy a check using the manual measuring sticks might be called for.
Jet liners have a fuel flow indicating system which is independant of the fuel qty system. This displays the amount of fuel being used by each engine as well as the total consumed by each engine (it is zeroed before engine start). At the end of the flight the crew can add up the fuel used by each engine and the total should compare closely with what the qty indicators show was burnt on the flight. A significant discrepancy required further checks during the next refuelling.