When the in timely yun water star or mountain star locates in the centre section (hall) of the xuan kong flyingstar nine-hall diagram for the building, the terminology is named "flyingstar trapped imprision". 飛星入囚,  凡當元之山星或向星飛入中宮，名「入囚」
For example, during the three-yun period, a building is constructed for:
1) xu-chen facing, the xuan kong flyingstar nine-hall diagram would reflect the in-timely yun water star appears at facing front hall, and the in-timely yun mountain appears at the sitting back hall, this is named "on-water-on-mountain" symbolises prosperity for wealthy and healthy, provided the surrounding environment matching accordingly.
However, once the three-yun over then enters into four-yun, the four-yun mountain star appears at the centre hall instead of at the appropriate location in the sitting back side, this symbolises the residents' life would be having health, safety problem, bad luck for increasing and retaining family members.
2) chen-xu facing, the xuan kong flyingstar nine-hall diagram would reflect the in-timely yun water star appears at facing front hall, and the in-timely yun mountain appears at the sitting back hall, this is named "on-water-on-mountain" symbolises prosperity for wealthy and healthy, provided the surrounding environment matching accordingly.
However, once the three-yun over then enters into four-yun, the four-yun water star appears at the centre hall instead of at the appropriate location in the facing front side, this symbolises the residents' life would be having financial problem, bad luck in money.
As such, you can see in above example, the three-yun constructed building would have at most 20 years of luck within the three-yun period of time.
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