Sixty Nine..you might find it important to know, that the "Altitude" your Phantom shows is actually a number calculated from barometric pressure. It really has nothing to do with the actual position of the ground (OR WATER) underneath your bird.
Weather conditions notwithstanding, barometric pressure has to do with the weight of all the air above you weighing down on you. Think of it as a stack of air from the ground up to the sky. That stack of air is heaviest at ground level, and becomes slightly lighter as you move up, IE the stack above you becomes slightly shorter.
At sea level that stack of air theoretically weighs 14.7 pounds per square inch. (Barometric Pressure) Your bird measures that pressure and calculates around about, maybe, possibly, it thinks, somewhere in the vicinity of where sea level is.
Weather conditions affect the barometric pressure too, but the bird does not use that information to make any corrections. The bird 'altitude' is more useful to tell if you are 100 feet above land or 250 feet above land. And it is better used as a relative measure rather than absolute.
IE: if on the ground, it reads 10 feet , then when it reads 30 feet you are probably pretty close to 20 feet up.
