Accuracy of the fuel gauge

I filled my car 4 times since I have it and I noticed a slight difference between what the computer gives me as the average fuel consumption and what I get when I use the data from the odometer and the liters required to fill the tank.

I guess that this gap might be caused by the imprecision of the fuel gauge. If I forgot the first data (Breaking period) the difference represent a 4 to 6 % drift which is "acceptable".

What is a little disturbing is that the last time I filled the tank, the computer estimated the "Distant Until Empty" to be 23 kilometers (which should represent 1 or 2 liters with a fuel consumption of 4.5 L/100Km) but It took 36,2 liters to fill the tank which has a 45 Liters capacity. I should have been able to drive for another 200 Km with the remaining 9 liters !


What might explain this gap and what should I do with it ?