经曰∶凡寸关尺者。脉之要会也。从关至尺是尺。内阴之所至也。从关至鱼际是寸口。
内阳
九分
反
盖取命之根本。然后及于身而言之也。凡十二经脉有病之时。先于尺泽寸口见之。故尺寸者
。是脉之要会也。从关至尺是尺。内阴之所治者。夫三部之脉。取中而上下分之。从关中至
尺泽为内。是属阴。故言内阴之所治也。言尺泽者。尺脉一寸之外。余脉下入不见。如入深
泽而沉。故曰尺泽也。凡诊者。若寸口关脉不见。惟尺脉在者。其人必不死。亦如树之有根
。枝叶虽枯。其根气元活。故寸、关者枝叶也。尺泽者根本也。从关至鱼际是寸口。内阳之
所治者。夫自关而向上分之。上至寸口。故言关至鱼际者。是长骨后际。如鱼之颈际。故曰
鱼际也。言从关上至鱼际。下占一寸属阳。是内阳之所治也。然寸口虽占一寸。而脉见九分
者。言阳数奇阴数偶故也。是以关前属阳。故言九。奇也。关下属阴。故言寸偶也。故分寸
为尺者。关以上虽取一寸。而脉见九分。故曰分寸。为其先取一尺而言。盖先从根本言之。
故一尺内取一寸。而脉一寸内取九分而诊之。故言分寸为尺。从尺而取寸。从寸而取分是也
。分尺作寸者。从关以下至尺泽也。盖取脉长一寸而诊之。其一寸之脉。盖先取一尺之分。
而其中除却九寸。而更取一寸用之。故言阴得尺内一寸。阳得尺内九分。从始至终。寸尺位
脉长一寸九分。此则尺寸始终之法也。凡寸后尺前。两境之内主于关。为寸关尺也。上部属
阳故法天。下部属阴故法地。中部阴阳相兼故法人。关者穿也。言上可以穿其天。下可以穿
其地。上下关通而取其中。故言关也。而分三部候天地人。以法三才也。凡古法定尺寸者。
皆先取一尺而言之。从尺而取寸。此则是其大纲也。又凡脉长短不同。其形各异。又曰。人
长则脉长。人短则脉短。据此言之。岂可执其一概。必在医者以意审详。今则以鱼际骨下为
寸口位。占九分。更下行一寸为尺部。合成一寸九分。中关为关部。以安三指。此之所定寸
关尺。盖根据难经。永为楷式。不可改移。
《黄帝内经》说：凡是寸、关、尺三部脉，是脉诊的关键汇聚之处。从关部向尺侧延伸的部分称为“尺”，对应体内阴气的所治范围；从关部向鱼际方向延伸的部分称为“寸口”，对应体内阳气的所治范围。
先探求生命的根本，然后才及于身体其他部位而言。当十二经脉发生病变时，往往先在尺泽和寸口处显现出来。所以寸和尺是脉诊的关键汇聚之处。从关部向尺侧延伸的是“尺”，这是阴气所治理的范围。
对于寸、关、尺三部脉，取其中部并向上下划分。从关部向尺泽方向为内部，属于阴，所以说这是阴气所治理的地方。所谓“尺泽”，是指尺脉在寸口之外的一寸范围内，其余部分的脉象向下深入而不可见，就像进入深潭一样沉潜，所以称之为“尺泽”。
凡是在诊脉时，如果寸口和关部的脉象摸不到，只有尺脉存在，那么这个人必定不会死亡。这也如同树木有根一样，虽然枝叶枯萎，但树根之气依然鲜活。所以，寸部和关部好比是枝叶，尺泽好比是根本。
从关部向鱼际方向延伸的是“寸口”，这是阳气所治理的范围。从关部向上划分，上至寸口，所以说从关部到鱼际的部分，位于长骨的后际，形状像鱼的颈部边缘，所以称为“鱼际”。指出从关部以上到鱼际，下方占据一寸的位置属于阳，是阳气所治理的范围。
然而，寸口虽然占据一寸的位置，但脉象实际显现的长度为九分，这是因为阳数为奇数、阴数为偶数的缘故。因此，关前属于阳，所以说是“九”（奇数）；关后属于阴，所以说是“一”（偶数）。之所以称“分寸为尺”，是因为关部以上虽然取一寸的范围，但脉象只显现九分，所以称为“分寸”。这是为了先从根本说起，所以在“一尺”的范围内取“一寸”，而在这一寸之中又取九分来进行诊察。所以说“分寸为尺”，即从尺部取寸，从寸部取分的道理。
将“分”和“尺”合成为“寸”，是指从关部以下至尺泽的部分。大概取脉长一寸来进行诊察。这“一寸”的脉，是先取“一尺”中的“分”，然后在其中除去九分，再取一分来使用。所以说“阴得尺内一寸，阳得尺内九分”。从头到尾，寸部和尺部的脉长总共为一寸九分，这就是尺寸定位的根本法则。
在寸部之后、尺部之前的两个区域之间，主要归属于关部，这就构成了寸、关、尺三部。上部属于阳，所以效法天；下部属于阴，所以效法地；中部阴阳兼具，所以效法人。关，意为贯通。指上部可以贯通天，下部可以贯通地，上下贯通而取其居中位置，所以称为“关”。并以此分为三部来候察天、地、人，以效法三才（天、地、人）。
凡是古代定寸、尺的方法，都是先取一尺来说明，从尺部取寸部，这是其大纲要领。另外，脉的长短各不相同，形态也各异。又说：人体高大则脉长，人体矮小则脉短。据此而言，怎么能拘泥于一种固定的标准呢？必须由医生用心仔细审察。
现在我们将鱼际骨下方定为寸口位，占据九分；再向下行一寸定为尺部，合起来共一寸九分；中间定为关部，用以安放三指。这里所确定的寸、关、尺定位，是根据《难经》制定的，作为永恒的楷模，不可更改移动。
The *Classic of Medicine* (*Huangdi Neijing*) states: The Cun (Inch), Guan (Bar), and Chi (Cubit) positions are the key convergence points of pulse diagnosis. From the Guan position towards the Chi side is the "Chi" position, corresponding to the realm governed by Yin Qi within the body. From the Guan position towards the Yuji (Fish Border, LU10) direction is the "Cunkou" (Inch Port) position, corresponding to the realm governed by Yang Qi within the body.
One must first seek the root of life before discussing other parts of the body. When diseases occur in the twelve primary meridians, they often manifest first at the Chize (Pool at the Elbow, LI11) and Cunkou positions. Therefore, Cun and Chi are the key convergence points of pulse diagnosis. The part from the Guan position towards the Chi side is called "Chi," which is the area governed by Yin Qi.
Regarding the three positions of Cun, Guan, and Chi, one takes the middle point and divides it upwards and downwards. From the Guan position towards the Chize position is the interior, belonging to Yin; hence it is said to be the area governed by Yin Qi. The term "Chize" refers to the fact that outside the one-cun range of the Chi pulse, the rest of the pulse sinks deep and becomes invisible, like entering a deep pool or marsh; thus it is called "Chize."
In general, when diagnosing, if the pulses at the Cunkou and Guan positions are imperceptible, but the Chi pulse remains palpable, the person will certainly not die. This is akin to a tree having roots: although the branches and leaves may wither, the vital energy of the roots remains alive. Thus, the Cun and Guan positions are like the branches and leaves, while the Chize position is like the root.
From the Guan position towards the Yuji (Fish Border, LU10) direction is the "Cunkou" position, which is the area governed by Yang Qi. Dividing upwards from the Guan position to the Cunkou, the section from Guan to Yuji lies behind the distal end of the long bone, resembling the neck border of a fish; hence it is called "Yuji." It is stated that from above the Guan to the Yuji, the lower portion occupying one cun belongs to Yang, representing the area governed by Yang Qi.
However, although the Cunkou occupies a space of one cun, the pulse manifestation is only nine fen (one-tenth of a cun). This is because Yang numbers are odd and Yin numbers are even. Therefore, the area anterior to the Guan belongs to Yang, hence referred to as "nine" (an odd number); the area posterior to the Guan belongs to Yin, hence referred to as "one" (an even number). The phrase "fen Cun as Chi" exists because although the area above the Guan takes up one cun, the pulse manifests for only nine fen. This is termed "fen Cun" (dividing the cun). This explanation starts from the root: within the "one chi" range, one takes "one cun," and within this one cun, one takes nine fen for diagnosis. Hence, it is said "fen Cun as Chi," meaning taking Cun from Chi, and Fen from Cun.
Combining "Fen" and "Chi" into "Cun" refers to the section from the Guan position down to the Chize position. Generally, one diagnoses a pulse length of one cun. This "one cun" of pulse is derived by first taking the "fen" from the "chi," excluding nine fen, and using the remaining one fen. Thus, it is said that "Yin obtains one cun within the Chi, and Yang obtains nine fen within the Chi." From beginning to end, the total pulse length of the Cun and Chi positions is one cun and nine fen. This is the fundamental method for positioning Cun and Chi.
Between the posterior boundary of the Cun and the anterior boundary of the Chi lies the Guan position, constituting the three positions of Cun, Guan, and Chi. The upper part belongs to Yang and follows the pattern of Heaven; the lower part belongs to Yin and follows the pattern of Earth; the middle part combines Yin and Yang and follows the pattern of Humanity. "Guan" means penetration. It signifies that the upper part can penetrate Heaven, and the lower part can penetrate Earth, connecting the upper and lower to take the central position; hence it is called "Guan." These three positions are used to inspect Heaven, Earth, and Humanity, following the concept of the Three Powers (San Cai).
Ancient methods for defining Cun and Chi always started by referring to one Chi, taking Cun from Chi; this is the general principle. Furthermore, pulse lengths vary, and their shapes differ. It is also said: If a person is tall, the pulse is long; if a person is short, the pulse is short. Based on this, how can one adhere rigidly to a single standard? Physicians must carefully examine each case individually.
Currently, we define the position below the bone of the Yuji (Fish Border, LU10) as the Cunkou position, occupying nine fen. Moving further down by one cun defines the Chi position, totaling one cun and nine fen. The middle position is defined as the Guan position, where three fingers are placed. The determination of the Cun, Guan, and Chi positions here is based on the *Nan Jing* (Classic of Difficult Issues) and serves as an eternal model, which should not be altered.