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Since the publication of Wang Shuhe's *Mai Jing* (Pulse Classic), Cui Jiayan of the Song Dynasty and Li Shizhen of the Ming Dynasty had their pulse rhymes widely circulated in the world. However, these works were all cumbersome and failed to grasp the essential points.

Zhongjing’s pulse methodology features a most crucial one-character key: "Huan" (Slow/Relaxed). Zhongjing stated: "The Yang pulse is Floating, Large, and Ru (Soft); the Yin pulse is also Floating, Large, and Ru. When the Yin pulse and Yang pulse are equal in degree, this is called 'Huan'." The Huan pulse is neither too fast nor too slow, circulating evenly between Ying Qi (Nutritive Qi) and Wei Qi (Defensive Qi), having neither excess nor deficiency. Extending from this to pulses of excess: if Wei Qi is excessive, it is called "Gao" (High); if Ying Qi is excessive, it is called "Zhang" (Chapter/Abundant); when Gao and Zhang contend with each other, it is called "Gang" (Cord-like/Taut). Regarding pulses of deficiency: if Wei Qi is weak, it is called "Bei" (Low/Inferior); if Ying Qi is weak, it is also called "Bei"; when these two Bei states contend, it is called "Sun" (Damaged/Depleted). These two categories are listed separately outside the Huan pulse to clarify the states of excess and deficiency. However, Chi (Slow) and Huan have subtle differences: Huan indicates harmonious Wei Qi, while Chi indicates harmonious Ying Qi. A pulse that is both Huan and Chi represents a balance of rigidity and softness, called "Qiang" (Strong). If Huan and Chi contend, it is called "Chen" (Deep). In diagnosing original pulses and pathological pulses, harmony between them constitutes the Ping Pulse (Normal Pulse); pathology is identified where they contend. This was the core principle articulated by Zhongjing. Regarding the differentiation of Exterior/Interior and Fu/Organ, although one generally looks at Floating, Deep, Slow, and Rapid pulses, combining these with Gao, Zhang, Bei, and Sun allows for the discrimination of Deficiency and Excess within Yin and Yang. Therefore, Da (Large), Floating, Rapid, Active, and Slippery are classified as Yang pulses; Chen (Deep), Choppy, Weak, String-taut, and Fine are classified as Yin pulses. By extending this logic, pulses such as Kou (Scallion-stalk), Ge (Leather), and Lao (Firm) vary in name but are distinguished by their contention to ascertain the cause of disease. Furthermore, by counting respiration during palpation, Dai (Intermittent), Jie (Knotted), and Cu (Rapid-intermittent) pulses can be deduced. Later pulse manuals followed this classification system. Yet, the profound intricacy here requires comprehensive understanding from top to bottom and exterior to interior. Without repeatedly discussing Zhongjing’s classic texts, how could one penetrate its subtleties?

The laws governing life, death, auspiciousness, and misfortune of the Five Zang and Six Fu organs depend solely on the Cun Kou (Radial Artery) pulse. Internal pulse theory assigns the Left Cun to the Heart and the Right Cun to the Lung. The *Nan Jing* (Classic of Difficult Issues) states: "The Cun Kou is the great assembly of pulses, the site of movement of the Hand-Taiyin Meridian." The Hand-Taiyin is the Lung Meridian. Why is emphasis placed solely on the Lung? It is because the Left Cun belongs to the Heart, which is the master of the body's Ying Qi; the Right Cun belongs to the Lung, which is the master of the body's Wei Qi. This represents a functional allocation of location. However, Ying and Wei Qi rely entirely on Gu Qi (Grain Essence) for distribution. Gu Qi enters the Stomach and transmits to the Lung, allowing the Five Zang and Six Fu organs to receive Qi. The clear portion becomes Ying Qi, and the turbid portion becomes Wei Qi. Ying Qi circulates within the vessels, while Wei Qi circulates outside the vessels. Ying and Wei Qi travel through the Yang aspects twenty-five times and through the Yin aspects twenty-five times to complete one cycle. After fifty cycles, they reconvene at the Hand-Taiyin. Every exhalation and inhalation originates from the Lung. Thus, the Lung serves as the gate of respiration and the master of Ying and Wei, effectively unifying two functions into one entity.

Regarding the Cun Kou pulse, Zhongjing first provided a sixteen-character golden needle mantra: "Floating indicates Exterior; Deep indicates Interior; Rapid indicates Fu organs; Slow indicates Zang organs." In terms of the human body, the back is Yang, the abdomen is Yin; the exterior is Yang, the interior is Yin; Fu organs are Yang, Zang organs are Yin. In terms of pulse appearance, the Cun position is Yang, the Chi position is Yin; Floating is Yang, Deep is Yin; Rapid is Yang, Slow is Yin. Since the Cun position inherently belongs to Yang, why can it also serve as the diagnostic site for Zang (Yin) diseases? Therefore, Zhongjing reiterated: "If the pulse is Slow, one knows the disease is in the Zang." From this, it is evident that not only should diseases of the Yang meridians be determined by the Cun Kou pulse, but even when pathogens move from Yang to Yin or directly invade the Yin meridians, the diagnosis via Cun Kou must not be neglected. With these sixteen characters as the outline, all other pathological pulses formed by contention can be extended and categorized to ascertain the location of the disease. This requires diligent study and familiarization in daily practice.