The compass on the geomantic compass is only a general guide and can only measure the magnetic direction of its position.
If you put a plate in the house, because there are steel bars on the walls and ceiling around the house, the electromagnetic waves emitted by the electrical appliances in the house can affect the magnetic field in the house, so measuring every point in the house with a compass is different. Just measure every point in the house with a compass. Even the direction of the gate, a foot or two before and after can give a completely different direction. So feng shui masters usually measure the orientation of houses outside.
The outdoor measurement is close to the geomagnetic north and south poles, but there will be deviations. The source is nearby buildings or mountains. The closer the distance, the greater the impact. The greater the wind, the greater the deviation.
Not to mention the north and south in latitude and longitude, it is only a theoretical standard, unless it is measured by professional tools and methods.