Weird magnetometer values

[wibble]

How much variation do you expect between runs? This is for a BH:

mobian@mobian:/sys/bus/iio/devices/iio:device3$ cat sampling_frequency
80
mobian@mobian:/sys/bus/iio/devices/iio:device3$ python3 ~/src/magnetometer_test/magnetometer.py
Starting measurements. Press Ctrl-C to quit
x 502.22 y 72.19 z -2621.09 ^C
Offsets: x -5566.0 y -2614.0 z -885.0
Weights: x 0.9695375849222003 y 1.0616750659947205 z 0.9740202553940995
Finished
Global minima/maxima:
xmin -8608.00 xmax -2524.00 ymin -5392.00 ymax 164.00 zmin -3913.00 zmax 2143.00
mobian@mobian:/sys/bus/iio/devices/iio:device3$ python3 ~/src/magnetometer_test/magnetometer.py
Starting measurements. Press Ctrl-C to quit
x 573.87 y -1594.59 z -2108.91 ^C
Offsets: x -5616.0 y -2810.0 z -957.5
Weights: x 0.9826456049860305 y 1.0367913832199547 z 0.9824872414719312
Finished
Global minima/maxima:
xmin -8718.00 xmax -2514.00 ymin -5750.00 ymax 130.00 zmin -4060.00 zmax 2145.00

An interesting 'soft iron' element in the phone is the battery - I wonder if they vary enough to need recalibration on battery change?