been out this afternoon, did a compass calibration,took off did a flight and brought it down. then walked over to my car with every thing still switched on, put the phantom in my boot looked at the ipad screen and it says I had a compass error. I did another compass calibration near my car and it kept saying compass failed. is this because I was too close to my car ? (I was about 6 foot from the back of the car) how far do you need to be away from the car if this is the problem ?