I'm a new P3 pilot with only about a dozen flights on it, but have flown electric helis for last 6 years. I've started reviewing my flight data playbacks just to check for any possible error messages and noticed something peculiar with my altimeter (Height on playback). I start the flight at 0 feet but when I land in the same location after a 15 min flight or so, the altimeter shows anywhere from 10-30 feet. It appears to be biasing the altitude higher during the flight. Two questions: 1) Has anyone observed this and have a suggestion?; and 2) Does the RTH use this "height" for RTH fly back altitude and landing? Haven't used RTH yet but would like to know it will work (with this apparent increasing altitude bias) if I ever need it.