with considerable time as a trainer on A310 i insist that despite the FMS fuel predictions must be checked against 'paper' values in normal circumstances, and basic data (FF, FQI) used during non std config.
on 'normal' flights there is a discrepancy between fuel predictions and flight plan values which null out as the flight progreses. this despite the perf factors being incorporated in the FMC, this for instance could cause problems when checking trip fuels for lower levels.
observing the fuel predictions during a long hold (1 hr +) can be quite instructive - the values keep changing, and much more than expected changes due to changes in holding altitude.
i do remember being told to trust the equipment' many aeons ago, i guess the manufacturer has probably moved away from the simplistic 'trust the equipment' statement especially on these early glass cockpit aircraft.