As stated above: Under normal conditions, the Home Point altitude is recorded at engine start. It is based on AGL (Above Ground Level at your present position). So at your home point the Phantom's altimeter is set to "0" AGL. Even if you are on top of a mountain. The RTH fly home altitude is set by you, but can not be less than 30 meters (98 Feet). As you ascend, the telemetry altitude will also go up based on the Home point Altitude recorded at Engine Start. If you are flying below 30 meters and initiate RTH, the Phantom will climb to the preset altitude of 30 meters and come home. If you are flying above 30 meters, the phantom will stay at that altitude and come home. It will not descend until in a hover over the Home Point. I'm referring to my P3P.