Mine can tell if I'm sitting next to it's desk or not. I've come to the conclusion it's the deformation of the ground the desk is sitting on.
It's really a silly amount of precision for what I use it for. But It's so fun to lock g on .0000, even if only for a few seconds. Anyone who has a target of a specific amount of 0s can do it themselves. After the first 2 shits pretty random.