Thank You for your response,
I did calibrate it and saved the calibration, but do you mean that before I start I have to wait until the calibration state value is 0b111111 ?
I don't have any varying magnetic field source around the device, but is a piece of metal considered a source of changing mag. field?
I did the test again and that is the output [Heading] for each time I move the imu and bring it back to its initial position:
[130, 135.12, 135.06, 131.81, 130.4, 136.56, 137.6, 135.19, 136.25, 131.81, 135.31]
Still varies within 6 degrees in the same orientation.