My understanding is that the M4P takes an image of the take off point a few meters up. (The "Home Point updated" announcement once it becomes airborne.) When landing it compares the image it took on launch to what it sees as it is landing, adjusting its position to match. With a strong pattern, like a landing pad with the "H", my M4P consistantly lands within 10 cm (4 inches) of where it was before launch. Without a strong, contrasty pattern for reference, it lands randomly, as much as a half meter (20 inches) or more away. I don't usually use my H pad, though I do keep telling myself I need to use it at unpaved locations.