[pooh]

Maybe this could help you. How many bars when the car is full....12 you said? Just divide the total number into fourths....each fourth representing a quarter of a tank. You know how many gallons your gas tank holds.

It's not foolproof, but could give you at least an approximation. Maybe that's what you're doing at this time, I don't know. My Hyundai tells me how many miles I've gone and approximately how many miles I can still go. When that figure (how far I can go) gets to the point where I feel more petrol is needed, off to the gas station.