For anyone listening to Kruse regarding the whole magnetic fields thing, I won't stick oar in at all but here's a little thing many don't know.
When drilling an oil well, we need to know the direction and we use magnetometers. The local magnetic field is used to calibrate and correct the readings to deviation from north. Due to gradual shift in magnetic pole, we would update local models with an airborne gravimetric survey once or twice per year to keep the correction factor up to date.
That was then, like a while ago. Then some operators started doing it slightly more frequently cause they were changing more frequently. Now it's once a week for some.
Food for thought. Ground might feel stable but lots going on
