I live in a major city with many skyscrapers. I usually fly nearby (as in within 5 miles). I have read through all of the compass guides and know that I should not be re-calibrating every flight. But my DJI app requires me to, and usually I have to try the calibration 4-5 times before getting a signal. I am not flying directly near any buildings and always in open areas, but maybe it possible that being in an urban area simply causes these errors?