I have added a whirl to a Van Gogh, to illustrate this post. I pushed my magnetometer's performance today, by (relatively speaking) isolating its internal "modules" from each other. This worked. Now I said that I would only know what the magnetometer was for once I had built it. Pushing its sensitivity today, I now discover that a footstep on the floor registers on the magnetometer. OBSERVATION: My explanation: we are surrounded today by magnetised objects. A footstep disturbs them sufficiently to distort the magnetic "layout" of a room. I had never really imagined this existed.