I rely on the number scale rather than the blocks/bars
This is pretty much it. There is a float in the tank and that float cannot go higher than the level mechanically set by the armature its on. Even if you fill past that point the float will remain at its highest point, meaning your gauge will say on full until the float can drop. The worst case scenario with this (unlikely mind you) is that over filling will cause the armature to bend upwards as the float tries to float to the higher fill level. This will then mean you show was empty when you actually have much more fuel left in the tank.An interesting thing happened when I first filled my Duster to the third cut off so presumably full. I did nearly 200 miles before the gauge showed any fall in level then it fell as the mileage racked up. Next time I only filled to the first cut off and gauge started to fall as it should. My theory is that the tank is closer to 60 litres, to allow for expansion and foaming, but the gauge is calibrated to read 50 litres when full. So if you wedge your tank to the brim the gauge won't register a fall until you get below 50 litres. From now on I don't fill beyond first click.