Hello all - I have been flying my Phantom 2 Vision+ V2, many flights, with great results, since October. Did upgrade to the new compass, and the new RC with the thumbwheel, am flying the 9450 props, and ALL software and firmware are current as of this date. What I am experiencing is not a big problem, but more than an annoyance, in that Phantom flies really well, trustworthy, etc. The only issue I am having is that after a fully proper pre-flight routine, altitude displayed on my iPhone in the vision APP most often indicates -345 ft. Upon the advice on this and other forums, I then power-cycle Phantom, and sometimes altitude comes closer to reality, again pre-flight, but typically, I have to take off and fly for 5 minutes or so, bring Phantom back home, land, and power-cycle again, at which point altitude becomes closer to reality. Any thoughts or suggestions?