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Keqi (Guest Qi) refers to the "Zhenghua" (Direct Transformation) and "Duihua" (Opposite Transformation) of Yin and Yang on Earth, which superimpose upon Zhuqi (Host Qi), constituting the six stages of Keqi. The movement of Heavenly Stems initiates Yun (Movement/Transport), while Earthly Branches initiate Qi (Qi/Energy). For example, in the Zi (Rat) and Wu (Horse) years, Shaoyin Junhuo (Lesser Yin Sovereign Fire) governs the Sky (Sitian), and Yangming Zaojin (Greater Yang Dry Metal) governs the Earth (Zaiquan). Qi ascends from below, so calculation begins with Yangming Zaojin located below: Yangming Zaojin generates Water; thus, the first stage of Guest Qi is Taiyang Hanshui (Greater Yang Cold Water). Water generates Wood; thus, the second stage is Jueyin Fengmu (Extreme Yin Wind Wood). Wood generates Fire; thus, the third stage is Shaoyin Junhuo (Lesser Yin Sovereign Fire). Fire generates Earth; thus, the fourth stage is Taiyin Shitu (Greater Yin Damp Earth). When three Yins reach their peak, one Yang is born (the Zhen Trigram), which is Shaoyang Xianghuo (Lesser Yang Ministerial Fire); therefore, Shaoyang Xianghuo is the fifth stage of Guest Qi. Taiyin Shitu generates Metal; thus, Yangming Zaojin is the sixth stage of Guest Qi. Other years follow this pattern. Therefore, in Chou (Ox) and Wei (Goat) years, the first stage of Guest Qi is Jueyin Fengmu, the second is Shaoyin Junhuo, the third is Taiyin Shitu, the fourth is Shaoyang Xianghuo, the fifth is Yangming Zaojin, and the sixth is Taiyang Hanshui. In Yin (Tiger) and Shen (Monkey) years, the first stage is Shaoyin Junhuo, the second is Taiyin Shitu, the third is Shaoyang Xianghuo, the fourth is Yangming Zaojin, the fifth is Taiyang Hanshui, and the sixth is Jueyin Fengmu. In Mao (Rabbit) and You (Rooster) years, the first stage is Taiyin Shitu, the second is Shaoyang Xianghuo, the third is Yangming Zaojin, the fourth is Taiyang Hanshui, the fifth is Jueyin Fengmu, and the sixth is Shaoyin Junhuo. In Chen (Dragon) and Xu (Dog) years, the first stage is Shaoyang Xianghuo, the second is Yangming Zaojin, the third is Taiyang Hanshui, the fourth is Jueyin Fengmu, the fifth is Shaoyin Junhuo, and the sixth is Taiyin Shitu. In Si (Snake) and Hai (Pig) years, the first stage is Yangming Zaojin, the second is Taiyang Hanshui, the third is Jueyin Fengmu, the fourth is Shaoyin Junhuo, the fifth is Taiyin Shitu, and the sixth is Shaoyang Xianghuo.

Zhuyun (Host Movement) refers to the five stages of Host Movement that remain unchanged each year. Wood is the first movement, transitioning after the Major Cold solar term at the beginning of the year; Wood generates Fire, so Fire is the second movement, transitioning after the Spring Equinox; Fire generates Earth, so Earth is the third movement, transitioning after the Grain in Ear solar term; Earth generates Metal, so Metal is the fourth movement, transitioning after the End of Heat solar term; Metal generates Water, so Water is the fifth movement, transitioning after the Beginning of Winter solar term. Each movement governs slightly more than 73 days and 5 ke (a traditional unit of time), which is the constant rule for every year.

Keyun (Guest Movement) is determined by the harmonization and transformation of the Ten Heavenly Stems. Years of Jia and Ji are Tu Yun (Earth Movement); years of Yi and Geng are Jin Yun (Metal Movement); years of Bing and Xin are Shui Yun (Water Movement); years of Ding and Ren are Mu Yun (Wood Movement); years of Wu and Gui are Huo Yun (Fire Movement). This is the Zhongyun (Central Movement) superimposed each year, starting the sequence from the Central Movement. For instance, in Jia and Ji years, Tu Yun dominates, so Earth is the first movement; Earth generates Metal, so Metal is the second movement; Metal generates Water, so Water is the third movement; Water generates Wood, so Wood is the fourth movement; Wood generates Fire, so Fire is the fifth movement. In Yi and Geng years, the first movement is Metal, the second is Water, the third is Wood, the fourth is Fire, and the fifth is Earth. In Bing and Xin years, the first movement is Water, the second is Wood, the third is Fire, the fourth is Earth, and the fifth is Metal. In Ding and Ren years, the first movement is Wood, the second is Fire, the third is Earth, the fourth is Metal, and the fifth is Water. In Wu and Gui years, the first movement is Fire, the second is Earth, the third is Metal, the fourth is Water, and the fifth is Wood. These are the changing Keyun of each year. However, Yi, Ding, Ji, Xin, and Gui belong to Yin Stems, known as the Five Yin Years, representing movements of deficiency (Buji); Jia, Bing, Wu, Geng, and Ren belong to Yang Stems, known as the Five Yang Years, representing movements of excess (Taiguo). This is the principle of Yin being deficient and Yang being excessive.

The aforementioned Zhuqi, Keqi, Zhuyun, and Keyun represent the constants of the four seasons and are insufficient for predicting extraordinary changes in Heaven and Earth. Shen Kuo stated: "Cold, heat, wind, rain, water, drought, locusts, and grasshoppers generally have fixed laws, and human diseases also fluctuate with the prosperity and decline of Qi and Yun, yet these methods often fail. Why?" This is because people adhere rigidly to fixed rules without knowing how to apply them flexibly. Suppose Jueyin is in charge; its Qi is predominantly windy, and people suffer from damp diarrhea. Does it mean the whole world is windy? Do all people suffer from damp diarrhea? Even within a single county, rainfall can differ. Where is the Qi and Yun in such cases? It is impossible to avoid errors. Generally, physical principles have both constants and variables. What Qi and Yun govern are constants; what differs from what is governed are variables. Constants resemble the intrinsic Qi; variables are ubiquitous and have specific correspondences. Thus, their manifestations include Cong (Following), Ni (Reversing), Yin (Excessive/Lax), Yu (Stagnant), Sheng (Overcoming), Fu (Retaliating), Taiguo (Excess), and Buji (Deficiency). Their occurrences vary. If Jueyin is in charge and windy, causing vegetation to flourish, this is called "Cong" (Following). If the sky is clear and clean, dry but windless, this is called "Ni" (Reversing). If the vast sky is hazy with dust and flowing water does not freeze, this is called "Yin" (Excessive/Lax). If strong winds break trees and clouds/dust are turbid and chaotic, this is called "Yu" (Stagnant). If mountains and marshes are scorched and vegetation withers, this is called "Sheng" (Overcoming). If extreme summer heat roasts like fire and locusts cause disaster, this is called "Fu" (Retaliating). If earthquakes occur and dust haze appears frequently, this is called "Taiguo" (Excess). If it is gloomy and cold without cessation, and heavy clouds darken the day, this is called "Buji" (Deficiency). Diseases and disasters respond to these changes based on the local climate conditions at that moment. Even within a few miles, if the climate differs, the corresponding outcomes differ completely. How can one cling to fixed rules?

During the Xining era, the capital suffered prolonged drought, and prayers were exhaustive. For several consecutive days, it was overcast, and people believed rain was imminent. Suddenly, one day it cleared up, with blazing sun. I entered the court for an audience due to official business. The Emperor asked when it would rain. I replied, "The signs of rain are already visible; it will rain tomorrow." Others argued that despite recent humid overcast weather, there was no rain, and now with such dryness, how could rain be expected? The next day, it indeed rained heavily. At that time, Shitu (Damp Earth) was in charge. The consecutive cloudy days indicated that the Cong Qi had taken effect, but it was overcome by Jueyin (Wind Wood), preventing rain. The subsequent sudden clearing indicated that Zaojin (Dry Metal) had entered the phase, overcoming Jueyin, allowing Taiyin (Damp Earth) to extend its influence. The Qi and Yun for the following day were favorable, hence the certainty of rain. This is an example of local prediction. If conditions differed elsewhere, the predictions would differ. The subtlety of this method is extremely precise. By deducing from this, one can attain the highest truth. Shen Kuo considered both Host and Guest as constants, treating what is observed locally and temporally as the variable, thereby deeply grasping the flexible methods of Huangdi and Qibo. Regarding Shao Bian's "Supplement to Omen Reading," the fifteen items are criticized for being too rigid and failing to fully capture the variations of Qi and Yun, so they are not recorded. The responses regarding Excess, Deficiency, Excessive, Stagnant, Following, Reversing, Overcoming, and Retaliating should still be sought in the *Neijing* (Inner Canon).