The Old Gas Tank

I had a Caravan some years ago and, while traveling through the mountains, the fuel pump pooped out. It was an interesting trip to say the least - me and 2 dogs on our way to a dog show from MI to Virginia Beach. Anyway, since this was a question that had been bugging me, when the pump was fixed and the gas tank was reassembled, I watched the gas gauge as gasoline was added to the empty tank. I was very surprised to see that the needle didn't even start to move upwards until 4 gallons had been replaced! Sure hope my new van has the same stamina!