Compasses are used for standing and things like that, not compasses. If you want to determine the north-south direction, you can consider not being disturbed, plus the magnetic declination.
When the compass is upright, the magnetic field is different in every place and position in the room. It doesn't care about the north-south direction, but about which house, which divination and which mountain each place falls in under a specific magnetic field environment, and then analyzes the geomantic problems according to these.