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The measurement of needle insertion depth is transmitted through the middle finger. By bending the middle joint of the middle finger, the distance between the tips of the two transverse creases constitutes one Cun (Chinese inch). For males, use the left hand; for females, use the right hand; for children, this method applies regardless of gender. One must assess the meridians according to the individual's height and body constitution (fat or thin).

[Note] The method for determining needle insertion depth is based on the *Tongshen Cun* (Body-Breadth Inch) system. Males use the left hand, females use the right hand. By flexing the second segment of the middle finger, the distance between the tips of the two creases is defined as one Cun, which also applies to children. Although people vary in stature and body build, leading to different insertion depths, those with taller frames have longer finger segments, while those with shorter frames have shorter segments. By adjusting the measurement according to the length of their finger segments, the accuracy will naturally be achieved. Individuals with thick muscles and abundant Qi and Blood should receive needles inserted to a depth of 3.5 Fen (one-tenth of a Cun); individuals with thin muscles and less robust Qi and Blood should receive needles inserted to a depth of 2 Fen. However, even so, one must apply flexibility (*Jing Quan*, principle and flexibility), avoiding rigid adherence to fixed rules. For persons of average build, the depth should be酌情ly determined within the range of 2 to 3 Fen.

Well (Jing) points are where Qi emerges, Stream (Ying) points are where it flows, Shu (Shu) points are where it pours, Jing (Jing) points are where it travels, He (He) points are where it converges, and Yuan (Yuan) points are its source. In Spring, Ying points are indicated; in Summer, Shu points are indicated; in Autumn, He points are indicated; in Winter, Jing points (and Jian points, referring to specific applications or variations) are indicated. For Zang organ diseases, Shu points are needled; for Fu organ diseases, He points are needled; for diseases of both Zang and Fu organs, Yuan points may be needled. Generally, the muscle tissue around Jing points is shallow, and deep needling is traditionally contraindicated.

[Note] Jing, Ying, Shu, Jing, He, and Yuan are the names of acupoints on the twelve meridians. The Yang meridities of the hands and feet possess Yuan points, whereas the Yin meridities do not have separate Yuan points; the Shu point of a Yin meridian serves as its Yuan point. "Where it emerges" is the Well (Jing), likened to water springing forth; "where it flows" is the Stream (Ying), likened to a small stream; "where it pours" is the Shu (Shu), likened to water pouring in; "where it travels" is the Jing (Jing), likened to a flowing river; "where it converges" is the He (He), likened to waters meeting; and "Yuan" is likened to the source of water. Needling Ying points in Spring targets collaterals located between the muscle bundles, requiring shallow insertion. Needling Shu points in Summer targets fine collaterals (Sun Luo) above the skin and muscle. Needling He points in Autumn also targets collaterals between muscle bundles, similar to Spring. Needling Jing points in Winter targets the area below the fine collaterals, requiring deeper insertion and retention because Cold Qi enters the Zang organs during winter. Both Jing and Yuan points are suitable for needling various diseases across all Hand and Foot Yin and Yang meridians, though depths vary and cannot be exhaustively listed. This represents the general principle of seasonal acupuncture, passed down since ancient times.