@zukeni
If you have problems with magnetic interference, calibration is not going to fix that.
- A wire carrying electric current will produce a magnetic field with closed field lines surrounding the wire.
- The closer to wire the stronger the field
- Right hand rule - thumb points current flow, fingers grabbing wire are field lines
- Field strength depends on current
From that you know that magnetometer should be far from high current lines, and that you can redirect magnetic field by twisting wires.
Imagine wire horizontally, placed below magnetometer, right hand rule you can see magnetic field lines hitting magnetometer. Now you twist the same wire, so your magnetic field becomes like ellipsoid stretching in the direction of wire. That way there is weaker field hitting magnetometer.