In San Yuan Xian Kong feng shui science, there is a terminology "chu gua" which means exceeding the control of the main trigram. The phrase "chu gua"  could be traced back to the source from a classical feng shui literature <tian yu jiang> wriiten in ancient China Tong dynasty. 
As per the Flyingstar stream, there are 8 ranges of luopan degrees should not be used for the facing direction for yin and yang mansions due to the concerned directions are unable to obtain pure qi from the main trigram but the qi is a mixture from the main trigram with the nearby trigram.
When a mansion is taking the kind of impure qi mixed and mess from two trigrams,  it would result the residents in the mansion to become often indecisive, making mistakes, messing up, disagreement with each other, health problem, etc kind of bad luck.
These 8 ranges are as follows:     
Luopan Degrees   The two trigrams involved
1) 19.5-25.5                Kan  Gen
2) 199.5 - 205.5         Li   Kun
3) 289.5-295.5           Qian  Dui
4) 109.5-115.5           Xun   Zhen
5) 334.5-340.5           Kan   Qian
6) 64.5-70.5               Zhen   Gen
7) 154.5-160.5          Li    Xun
8) 244.5-250.5          Dui    Kun
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