[MrEldritch]

This is true, and a valid point. The way they phrased it does make me feel more than a little suspicious, nonetheless.

(Besides, there's some other oddity there, like that apparently the alignment only matters when the magnetic field is calm)

[petschge]

When the magnetic field is non-calm that is probably due to a space weather event that is geo-effective and inducing large currents in the ground. The local magnetic field an then be significantly distorted depending on local conductivity. So to me that is not an oddity.

[austinjp]

You're right to still feel suspicious. Who's to say they didn't try 1,000 different post-hoc ideas? They declare only one, the may have been others. I'd be looking for preceding research and any published protocols, if I wasn't on mobile and didn't think it would be fruitless.