When I start the car even on an almost empty tank the gas needle reads full, pretty much 99% of the time. Once in a while it seems on long drives, the gas gauge finally decides it's too tired from sitting at the full line, and it starts to drop slowly to where I think the gas should be be, although I have caught it creeping back up to the full line to while driving. When I get to my location, after the car has been sitting, and then start the car back up again it shoots right to full again.
........Not knowing how much gas you have is annoying!!