Drive until the fuel gauge reads 1/2, refill car to full and note how many litres to fill it back to full. If it is between 30-40L (R33 tank is 65L, R34 is most likely similar) then its reading accurate, if not then its faulty.
If it is faulty then just note how many kms you get to a full tank. Fill car up and reset the tripmeter, drive car for about 200km and then refill the car. Note the total litres to fill car back to full and work out how many kms from a full tank (Tank capacity / Fuel To Fill * Kms Traveled = Kms from a Full Tank) , take about 50-100km off this number and reset the tripmeter whenever you fill the car up and remember to get more petrol whenever the tripmeter reads the designated kms.
It becomes second nature after a while