One issue I'm familiar with (from working for a government department that handles standards and regulated measures) is the effect of ambient atmospheric conditions on fuel density.
Both ambient temperature and air pressure (well, they're technically both the same, but a 20 degrees Celsius day at sea level is different to a 20 degrees Celsius day at 900m ASL, hence I kept them separate, and likewise, direct sunlight etc.) affect the density of liquid fuels. Your fuel gauge will read lower when it's -10 degrees Celsius than when it's 35 degrees Celsius, even though you still have the same amount of fuel. (In my country, petrol bowsers are allowed an error margin of 0.5% of delivered volume to allow for differences caused by ambient conditions) so if you can fill your car's tank when it's below freezing, you'll get a little more fuel than you would on a hot day - in places with extremes of climate, they tend to incorporate temperature compensators to avoid giving away too much free fuel :D
Also, fuel tanks are rarely a basic cuboid, so volume change is often non-linear due to shape / angles of faces etc.
Fuel levels can be measured a lot more sensitively, as you'll find in aircraft, but even then they measure consumed fuel as a primary indicator with fuel gauges secondary.
Both ambient temperature and air pressure (well, they're technically both the same, but a 20 degrees Celsius day at sea level is different to a 20 degrees Celsius day at 900m ASL, hence I kept them separate, and likewise, direct sunlight etc.) affect the density of liquid fuels. Your fuel gauge will read lower when it's -10 degrees Celsius than when it's 35 degrees Celsius, even though you still have the same amount of fuel. (In my country, petrol bowsers are allowed an error margin of 0.5% of delivered volume to allow for differences caused by ambient conditions) so if you can fill your car's tank when it's below freezing, you'll get a little more fuel than you would on a hot day - in places with extremes of climate, they tend to incorporate temperature compensators to avoid giving away too much free fuel :D
Also, fuel tanks are rarely a basic cuboid, so volume change is often non-linear due to shape / angles of faces etc.
Fuel levels can be measured a lot more sensitively, as you'll find in aircraft, but even then they measure consumed fuel as a primary indicator with fuel gauges secondary.