So today's flight made me wonder how they will enforce the 400' rule. When you take off from your location it's considered ground 0. Assuming you're in a flat area then your 400ft limit should be easy to maintain. How about if you climb a mountain? I flew up the side of a mountain behind the cabin. I was fairly close to the ground at the peak but my display shows an elevation of 980'. I was slightly above treeline at the peak so I was 100-200' above the peak of the mountain. Something to watch and I'm curious to see how the FAA will enforce this type of situation..