This morning when I parked at work the DIS showed that I had 300 od miles left in my diesel tank and the gauge was sitting pretty much on the half mark. When I went out for lunch I started the car up and it said I had 150 miles left in the tank and the clock was at a completely random time. The miles left in the tank usually stays the same as it was when I shut the car off or drops a little, but never that much. Also the fuel gauge hasn't moved. The miles in the tank didn't go back up but it was only a short drive. So I guess it might when I drive home (30 miles). Any idea what might have happened?