which method you are using to check average?????
try the below mention method:
I still use the old ""wagon driver method, shaking & taping the car while filling the tank fully""" to check average of my steermatic.
fill up the tank slowly & fully up to the neck, bring the meter to zero, drive it for couple of hundred KM's & than come back to same fuel pump & same guy repeat the same """old wagon driver """ method & than divide the mileage by liters.....& here you go with the exact average of your car.