What should I do if the compass on two or more different devices give me different headings? I tried to calibrate the compass on devices but anyway sometimes they show me differents headings.
Well, if 2 iOS devices give you 2 different readings then at least one of them has uncalibrated hardware. So is this a hardware question? I don't think there is much to do in terms of the program, especially if you have no idea what the exact skew is.