Ok hi guys im sorry if this subjuct has been covered already but ive been wondering about how the flight hight of the Phantom3 is worked out, because i fly in hilly country and im wondering when i set the return to home altitude,is this hight the altitude above ground level or is it worked on height above the controller itself? Thanks for any advice

Your Phantom has no way to sense what is below it.
All heights are relative to the take off point.
Home = zero