This should be old news, since the information is in the DJI manual (and one video), but the subject of iron and other ferrous metals is fresh in my mind and maybe the subject can stand a bump for those who are new to flying Phantoms - which I suspect is most of us. This morning I set out to do a test flight after replacing the compass on my Phantom (another subject). I was a little nervous about it, since this was the first time I've had my quad disassembled, so I went to my "test field." I do my practice and test flights there because it's a beautiful wide open flat space in the middle of nowhere with knee high grass for "emergency landings," and virtually zilch for wild wi-fi rf. There, my Phantom flew great, and held as placid a hover as I have ever seen it do. Whew! Then, down to business, I went 500 yards away to shoot a piece of machinery in a vineyard that can be best described as an iron stake farm. From the very start, the Phantom did about 10' toilet bowls - enough to really make me nervous, especially considering the new compass installation. I never felt like I was loosing control, but the hunting for position was pronounce enough that, had that been my first day or so flying the Phantom, I might have done something rash thinking that I was about to have a flyaway. Sooo...it was immediately back to the safety of my practice field for the next flight, where the Phantom flew solid as a rock again. Even though I was aware of the problem with iron, and kind of ready for it when I went to the vineyard, this incident proved to me beyond a doubt the significant effect ferrous materials can have on a Phantom's flight characteristics. Both these fields were in relatively close proximity of one another, identical except for the iron stakes, and the stability difference was significant. Something similar happened, by the way, about a month ago. The Phantom was doing fine until I set it on a small slab of concrete to take off from. This time I got an alternating yellow-red light, something I had never seen before, but I knew indicated a compass problem. This time, I shut it down and went home to check it out on the Assistant. I'd heard too many stories about red-yellow light combinations preceding a flyaway, and didn't want risk a flight to find out for myself. I'm sure it was just rebar in the concrete that was compromising the compass. Sorry this is so long. You knew all this, right? In any case, happy flying!