I’m curious - how does the fuel gauge work in cars? Does it have a little float in there to measure the level in the tank, or what? How does it compensate for the angle that the car is sitting at?
Also, does the technology exist to create a fuel gauge with a digital readout? It would be a vast improvement over the imprecise “E - F” scale now in use, but I’ve never seen a car with such a system.
I saw the inside of a fuel tank once. the measuring device was a lever with something that floats on the end.
It doesn’t.
Of course the technology exists, and you probably have seen it. The trip computer should be able to give you that information, or some more useful variant, like “distance to empty”.
A float attached to a varistor (variable resistor) in series with the battery and a coil creating an electromagnetic field twisting permanent magnets against the force of a spring which drives the needle of your guage (with some damping involved).
Dammit Desmo, on preview I see you’ve beaten me to it. Should’ve known you’d be on the boards at this time! 
Although on checking your link, Howstuffworks describes a guage that uses a bimetallic strip to drive the guage. The guages I’ve pulled apart were as above.
I see in the insides of fuel tanks all the time, and all the little bits and parts that go in them. Just bragging and nothing to contribute, BUT, it’s interesting that the “imprecise E-F scale” seems to be used in Spanish-speaking countries. They always seem to be amazed when I explain that E means “empty” and F means “full.”
Oh, “better” cars often do have a miles-to-empty feature, and often have cumulative and instantaneous mileage displays. The impreciseness of gauges has actually improved in years. It used to be that a near empty tank could cause your gauge to move all over the place on hills and fast curves. This isn’t the case so much any more since the gauges are electronic rather than a simple resistive circuit. They can be smarter about what they display.
I agree, the howstuffworks description of the guage is complete crap. Way out of date.
Relative to gas gauge accuracy, if you really want accuracy, just locate the level sensor in the precise center of the gas tank. Then slopes don’t matter.
If, and only if, the gas tank is symmetrical and smooth in two of the three axes it can be rotated through.
I had a Renault 11 ‘TX Electronic’ years ago, with digital fuel [and everything else] display, linked to a speech synthesizer that issued advice and warnings. Used to go nuts occasionaly and tell me the world was about to end, especialy when the tank sensor went wrong. Pulled it out and found the most complex gismo in the world. Put it back and forgot about it. Lived with the car telling me I was about to run out of fuel when I had just filled it up and staying silent when the tank was all but empty.
My Ford Escort’s fuel gauge can show almost empty when accelerating, but when I brake it goes up noticably. It seems that on my car the float is toward the front of the fuel tank.
>> A float attached to a varistor (variable resistor)
No a varistor is a different thing. This “variable resistor” is called a rheostat.
>> it’s interesting that the “imprecise E-F scale” seems to be used in Spanish-speaking countries. They always seem to be amazed when I explain that E means “empty” and F means “full.”
You’ll have to tell us what cars and what countries because in my experience cars in other countries are most often marked “0 - 1/2 - 4/4” . I guess you sa an American import.
What I want to know is how fuel gauges where the needle does not return to zero when the ignition is turned off work. The needle stays right there.
I’m not aware of a single, modern, automotive fuel tank that is anything close to symmetrical. Plus the float is attached to the pump, which is located where it’s convenient to the tank design and designers. The trend toward tank shapes is decidedly toward the more complex as they are crammed into smaller and smaller (and safer!) places. When you all finally see the new Mustang in the next year or so, for example, take a look underneath it and spot the fuel tank. Then you’ll remember that Balthisar said they were getting strange.
My 1989 Cadillac DeVille has a digital fuel readout. It reads F when full, E when empty, and a number indicating the number of gallons left in the tank anywhere in between (2-15). It also can tell you the instantaneous and average miles per gallon and the range left based on the current fuel level.
Digital instrument clusters were used in many cars a few years ago but lately seem to be fairly rare. I think they fell out of popularity because if one thing breaks you often end up having to replace the entire instrument cluster, which ain’t cheap.
Digital fuel gauge displays have been available in a number of cars for years. But you need to be aware that while a digital display or readout might be more precise than an analog display, it doesn’t make it any more accurate* because it’s merely representing information provided by an imprecise float/rheostat mechanism.
It seems what you really wanted to ask about was high tech precise/accurate gas tank gauge mechansims. It’s possible to design them, but at a such a prohibitive expense that there’s essentially no market for them. As previous replies indicate, there are a lot of factors to compensate for to get an accurate measurement of the amount of fuel in the tank.
*Difference between precision and accuracy: Precision is measuring in small increments. Accuracy is measuring correctly. A yardstick marked every 1/32" is more precise than one marked every 1", but if that first one has about three inches broken off at the zero end it’s a hell of a lot less accurate than the second one. However, it will give a wrong reading to the 32nd of an inch.