Im sure this has been asked before
Sadly, i may have even read the answer but i've forgotten.

What does the 20, 40, 60, 80 markings on the Fuel Gauge represent?

I thought it may have been "Litres of Fuel", but as i can easy fit more than 90 litres of Diesel in my X5, then the 80 at the Full mark, is kind of pointless.

Any ideas?