So recently I've ran into an issue with my fuel gauge not showing the correct amount of gas, specifically when it hits E there is about 4 more gallons in the tank and when it hits F there is about 2-3 gallons it doesn't show. I recently did a calibration test and noticed most of them don't seem exactly right. Am I right or just crazy? (attached YouTube link shows said test)

 

Looks like a normal test to me. I think the speedo only goes to 100 as that is how the test is set up.

And the gas gauge is never really accurate.... On my truck, when I hit an eighth of a tank, there is still 8 gallons in there. (34 gallon tank) I think that is done on purpose, to give you a bit of a 'reserve' capacity.

 

The float in the tank doesn't sweep right from the bottom to directly at the top. and since that little ball has a bit of height to it, even if it touches the top of the tank, it can't go any higher, which depending on the tank, can be a few gallons on either side. Same if it does touch the bottom. it can't go any lower and wouldn't read anything lower. Of course, to properly measure how much you would have at the top and bottom, someone would need to cut open a tank and see how much swing the flat has and then measure the capacity at the top and bottom. at the level that the float would stop.