No fuel gauge is completely accurate and no two fuel gauges are exactly identical. In other words YMMV (Your mileage May Vary).
That said: You really do not want to run your engine out of fuel. You do not want to try to push it to the limit, because someday you might go just go a little bit too far. I personally think that VW is making a big mistake (for the reliability of their cars) in advertising that you can get xxx miles per tank (depending on tank size/model). This tends to make people actually believe and try this. Mileage varies a lot depending on temperature, speed, tires, winds, terrain, time of year, fuel quality, etc. Fill up before you need to and driving stress goes way down. Enjoy driving instead of concentrating on mileage.
In town, where I know where all the best fuel stations are, I fill up immediately when my car tells me to. On the highway, where I do not know the area, I fill up when it gets below 1/4 tank (that last 1/4 tank goes pretty fast with my fuel gauge).
Have Fun!
Don