As long as the accurate reading can be taken, the instrument is acceptable. A surveyor's compass is fine. The time element is also considered. We actually only have to know the cycle and period the birthday falls into. The life-gua for each individual living in a house is calculated.
Reference is made to the adaptability of the individual to the bedroom.
Recommendations can be explained in terms of Wu Xing. Site study from the Form School of view is explained and recommendations that goes well with the surroundings are prescribed. In other words, no weird objects like a Bagua mirror, a sword or a flute will be used. Nothing is not explainable by logic. Pseudo-Feng Shui works only by chance.