In other words, during the Warring States period, there was a school that advocated the theory of Yin-Yang and Five Elements, called "Yin-Yang School", whose main representatives were Zou Yan and Zou Shuang of Qi. With the complexity and diversity of the world, the simple way of thinking that everything is dichotomous can no longer explain what is happening in front of us. Thus, a new way of thinking, such as "Eight Diagrams", is derived, which is used to express the movement and changes of Yin and Yang, and to express various natural phenomena, and can be used to calculate the passage of time, natural changes and various opportunities in life. The wise ancients then arranged the explanations of these phenomena into the Book of Changes, and the reference book handed down to this day in the Zhou Dynasty is the Book of Changes. The "Five Elements Theory" is developed from Jin Mu's theory that five basic substances, fire, water and earth, are "constantly changing in cycles". By studying the theory of Yin-Yang and Five Elements, we can draw up a calendar from the calculation of celestial movement and master everything in the world. Later, astronomers, calendar experts and five-element experts specializing in celestial bodies were developed.