Here are some plots for passes from the 16 Feb to 18 Feb over Europe.
The blue curve shows the calculated F vector from each magnetometer readings F = sqr (x^2+y^2+z^2)
The green curve shows the calculated F value in that particular height at the current position of GRIFEX (timestamp of the telemetry packet) – based on the WMM 2015 model.
There is a permanent magnet onboard that is providing a DC offset to magnetometer readings. The measurements are NOT cleaned up by the satellite, thus they have the DC offset. Also there is a time varying noise source from the solar panels and other current loops in the satellite.