I use a fuel stick to measure the fuel and put that information in my
fuel flow computer. I'm usually within a tenth of a gallon on landing.
Its pretty easy to make your own fuel stick, the best ones are wood.
I've made some out of the paint stir sticks you get at the home
improvement stores (they look like rulers). The best part about wood
is once you measure the fuel you just shake it and the fuel stain is
gone and ready for the next tank. The glass ones that you have to
stick your thumb in kinda suck.

-Robert