Sanyuan Jiuyun is a method to divide China time. It has been recorded in the Yellow Calendar since ancient times and used in combination with the dry calendar, which is mostly used for geomantic omen.
The Western Four Fates are numerology. According to the Sanyuan Jiuyun, people's divination can be divided into eight categories, such as seeing, Li, Zhen, Xun, Gan, Kun, Gen and Xun. Among them, the hexagrams such as Kan, Li, Zhen and Xun are called the four fortunes of the East in Yangzhai studies, while Gan, Kun, Gen and Hui are called the four fortunes of the West. I hope my answer is helpful to you.