Is the fuel gauge like the temperature gauge ?(not accurate)

Hello,

I had to run my van out of diesel to ship it and it was impossible. For the first half of the tank it went slowly down normally and then after a half it hardly moved. To get to where I was going I drove about 100 miles and went from around 3/4 to half. So I figured with the next 100 miles it would be at a quarter but it didn't happen.

I ended up doing my bit to save the planet by driving about 80 miles up and down a big long road and looping back at a roundabout ! I eventually got it to a quarter, gave up and said sorry to the shipping people who will now have to siphon it but they seemed to not mind at the idea of free diesel.

So is the fuel gauge known to be not very accurate in the lower readings ( the opposite of the temperature gauge )? My full is definitely full and I know it moves about a bit on slopes but why did my van suddenly go so economical ?

I don't want to run it out again but it would be nice to know if the bottom half of the gauge gives more than the top.