More accurate gas tank readings

The suggestion would work and should be fairly easy in a new car with a vehicle computer. Indeed, I expect they already do that if the fuel display is digital (suspect many analog gages today are actually a computer output). Many have long suspected that auto manufacturers design so that the fuel gage drops slower at first. Their benefit is that when people take a long test drive or rent a new model, they get the impression they are getting great mileage ("only used 1/4 tank"). John Q Public has no concept of non-linear response. He thinks if you double something, you always get double the result, that is simply "common sense".

I mainly care about "exactly where is empty". To determine mileage, I use the meter on the fuel pump. It probably doesn't shut off at the exact same volume when full, but that averages out over many repeats. Just write down the mileage on the gas receipt each time, or just reset your trip counter if you have one. If I fillup 19 gal and know I have an 18 gal tank, I report the station to the State's Measures and Weight Department.