Hi Josh, Indeed a GPS heading requires the device to be moving. The faster the device moves, the better the heading accuracy. Although very inaccurate at low speeds, the GPS heading has a clear advantage in that it does not drift. Of course for a stationary device, this is not useful. I'm still having a hard time figuring out your use-case. for 2 reasons: (1) "After various hours of runtime the magnetic calibration is seen to drop from 3 to 0 with no noticeable changes to the device's surroundings" > Your previous datalog proves otherwise, where the magnetometer offset changed dramatically. The most likely cause of this are electrical current in the vicinity of the sensor (For example, if the trace for supply current of the display backlight is near the sensor, it will cause a large offset change when the display turns off/on). Even your *good* datalog shows jumps in the magnetometer data that cannot be explained by rotation. > Both of your datalogs are standing still. If the device is at rest, what kind of motion are you measuring? What are the range of motions do you expect the device to experience ? o_o
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