How to use a cell phone feng shui compass? Is it trustworthy?

The cell phone compass is positioned by satellite, which is different from the traditional compass that relies on the earth's magnetic field to find the north and south. According to the satellite positioning we can accurately find the north and south poles of the earth, but according to the compass to find it will deviate a lot. This is called magnetic declination.

But, since ancient times, the geography of feng shui survey is based on the Earth's magnetic field to determine the direction. The ancients did not have a satellite, the record of the mountains and rivers is also so recorded. So the use of traditional geomancy compass survey geography is correct. To Baidu search Dongding compass there are many related articles.