What's the name of Chiang Kai-shek's geomantic omen?

The geomantic turtle used by Chiang Kai-shek is called "Gankun Geomantic Turtle". This is a square turtle shell with eight hexagrams engraved on it: Gan, Kun, Zhen, Xun, Kan, Gen, Li and Hui. Chiang Kai-shek believes that placing this geomantic turtle can adjust the environmental energy and improve the fortune and good or bad prediction ability. However, Feng Shui has no scientific basis, and its effectiveness needs further verification.