Hi Imran,

A few things here. One, it's impossible to use every drop of fuel in the tank without the car cutting out or running erratically, so you can never base your calculations on the quoted capacity of the tank. Every fuel system is different, but you need to allow for a few litres, potentially. Two, the quoted volume is certified at a certain temperature, as is the economy. Any drastic changes from that temperature will throw the calculations out. Finally, you just can't believe on-board computers, especially older ones...