Hope this is the answer!
Tank full; gauge reads 100%, set trip odo to zero. Drive until gauge reads 0%, read trip odo and you will used half a tank full, say it reads 125 miles so you can reset trip to zero and after 100 miles or so fill up! Seems gauge relates to half a tank only, so my dealer tells me and this way seems to work for me.
My build date was this February so its always possible others work differently. Bizarre ......
