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The method of Zi Wu Liu Zhu (Midnight-Noon Ebb-Flow) refers to the matching of rigidity and softness between Heavenly Stems and Earthly Branches, the harmony of Yin and Yang, and the opening and closing cycles of Qi and Blood in specific acupoints at designated times. Why are "Zi" (Rat hour) and "Wu" (Horse hour) used for this designation? Because at the beginning of the Zi hour (11:00 PM - 1:00 AM), Yang Qi begins to generate; and at the beginning of the Wu hour (11:00 AM - 1:00 PM), Yin Qi begins to generate. Therefore, dividing by Zi and Wu achieves a balance in the middle. "Liu" (Flow) means movement, and "Zhu" (Pour/Stop) means infusion or residence.

There are ten Heavenly Stems and twelve Meridians. Jia corresponds to the Gallbladder, Yi to the Liver; Bing to the Small Intestine, Ding to the Heart; Wu to the Stomach, Ji to the Spleen; Geng to the Large Intestine, Xin to the Lungs; Ren to the Bladder, Gui to the Kidneys. The remaining two meridians are the Sanjiao (Triple Burner) and the Pericardium (Bao Luo). The Sanjiao is considered the father of Yang Qi, and the Pericardium is the mother of Yin Blood. Although these two meridians differ from those associated with Ren and Gui, they are also distributed among the Ten Stems. Furthermore, within each meridian, there are five categories of acupoints: Jing-Well, Ying-Spring, Shu-Stream, Jing-River, and He-Sea, which correspond to the Five Elements Metal, Water, Wood, Fire, and Earth. Thus, the Jing-Well point of Yin meridians belongs to Wood, while that of Yang meridians belongs to Metal; the Ying-Spring point of Yin meridians belongs to Fire, while that of Yang meridians belongs to Water; the Shu-Stream point of Yin meridians belongs to Earth, while that of Yang meridians belongs to Wood; the Jing-River point of Yin meridians belongs to Metal, while that of Yang meridians belongs to Fire; and the He-Sea point of Yin meridians belongs to Water, while that of Yang meridians belongs to Earth.

Within the meridians, there is also the concept of "Returning to the Root and Restoring the Origin," which serves as the gateway for the entry and exit of the Twelve Meridians. Yang meridians have Yuan-Source points; when passing through the Shu-Stream points, they simultaneously pass through the Yuan-Source points. Yin meridians do not have separate Yuan-Source points, so the Shu-Stream points serve as substitutes. For example, the Jia Gallbladder meridian originates from Qiuxu (GB40), and the Yi Liver meridian originates from Taichong (LR3). Additionally, according to the *Qianjin Fang* (Thousand Gold Formulas), the six Yin meridians also have Yuan-Source points: Zhongdu (LR6) for the Yi Liver, Tongli (HT5) for the Ding Heart, Gongsun (SP4) for the Ji Spleen, Lieque (LU7) for the Xin Lung, Shuiquan (KI5) for the Gui Kidney, and Neiguan (PC6) for the Pericardium.

Therefore, on Yang days, Qi moves first and Blood follows; on Yin days, Blood moves first and Qi follows. When the time is appropriate, the acupoint opens; when the time is missed, it closes. Yang Stems inject into the Fu organs, namely Jia, Bing, Wu, Geng, and Ren. When a stem repeats (reappears), Qi is stored in the Sanjiao's Ying-Spring point and passes through the Yuan-Source point. For instance, when the Gallbladder (Jia) repeats at the Jia-Shen hour, Qi enters the Sanjiao's Ying-Spring point (belonging to Water). Since Jia belongs to Wood, Water generates Wood, referred to as "Jia combines and returns to transform into Wood." Similarly, when the Liver (Yi) repeats at the Yi-Wei hour, Blood enters the Pericardium's Ying-Spring point (belonging to Fire). Since Yi belongs to Wood, Wood generates Fire. All other cases follow this principle, based on the generation of Mother and Child elements and the mutual complementarity of Yin and Yang.

Yang days lack Yin hours, and Yin days lack Yang hours. Therefore, Jia combines with Ji, Yi with Geng, Bing with Xin, Ding with Ren, and Wu with Gui. Why does Jia combine with Ji? Because Wu and Ji in the Center belong to Earth, which fears being controlled by the Wood of Jia and Yi in the East. Wu is Yang Earth (older brother), and Ji is Yin Earth (younger sister). The older brother Wu marries off his younger sister Ji to the Wood family (Jia) as a wife, thereby achieving harmony between Yin and Yang without mutual harm. Hence, Jia combines with Ji. The same logic applies to the others. This concludes the explanation of the Zi Wu method.