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The measuring standards of all dynasties were based on the length of the Huangzhong (Yellow Bell, a standard pitch pipe used for calibration) but varied in their specific divisions. One method divided the length of the Huangzhong into nine cun (Chinese inches), with each cun consisting of nine fen (Chinese lines). This was the chi (ruler) initially created by Ling Lun under the command of the Yellow Emperor (Huangdi), known as the Ancient Law Chi or the Vertical Millet Chi. By selecting well-formed millet grains, the longitudinal length of one grain was defined as one fen; nine fen made one cun, and nine cun (totaling eighty-one fen) constituted one chi. Another method divided the length of the Huangzhong into ten cun, with each cun consisting of ten fen. This was the chi used when Shun unified the laws, measures, and weights, and it remained unchanged during the Xia Dynasty, hence named the Xia Chi. Legends state that Yu of Xia used ten cun per chi, referring to this ruler, also called the Ancient Degree Chi or Horizontal Millet Chi. By selecting well-formed millet grains, the transverse width of one grain was defined as one fen; ten fen made one cun, and ten cun (totaling one hundred fen) constituted one chi. A third method divided the length of the Huangzhong into four segments and added one extra segment to form a chi; this was the Shang Chi. It corresponded to 1.25 chi of the Xia Chi. Legends state that Tang Cheng (King Tang of Shang) used twelve cun per chi, referring to this ruler. A fourth method divided the length of the Huangzhong into five segments and subtracted one segment to form a chi; this was the Zhou Chi. It corresponded to eight cun of the Xia Chi. Legends state that King Wu of Zhou used eight cun per chi, referring to this ruler. A fifth method divided the length of the Huangzhong into nine cun and added one extra cun to form a chi; this was the Han Chi. The Tang Chi was identical to the Tang Cheng Chi but used by the Tang people, hence also called the Tang Chi. The Song Chi was identical to the Huangdi Chi but used by the Song people, hence also called the Song Chi. Among the aforementioned seven dynasties, there were five types of chi. The Vertical Millet Chi included the Huangdi Chi and the Song Chi; the Horizontal Millet Chi was the Xia Chi; the Diagonal Millet Chi was the Han Chi. Mutual verification among these provided supplements to the study of musical laws.

Cai Yuanding stated: In the Zhou Dynasty, both ten-cun and eight-cun rulers were used as chi. Using the ten-cun chi for measurement, ten chi made one zhang (Chinese foot), and ten zhang made one yin. Using the eight-cun chi for measurement, eight chi made one xun, and two xun (sixteen chi) made one chang. The *Shuowen Jiezi* states: "Ten cun is a chi, eight cun is a zhi." Thus, chi and zhi are names of two different instruments. Modern people only know that eight cun is a zhi, considering it the name of a separate object rather than a type of chi.

The *Book of Rites: Wang Zhi* states: "In ancient times, a step was eight chi using the Zhou Chi; now, a step is six chi and four cun using the Zhou Chi." (The *Wang Zhi* chapter was compiled during the reign of Emperor Wen of Han. Zheng Shizi noted: The term "Zhou Chi" here should likely be read as "Xia Chi." Chen Xiangdao explained: Six chi and four cun refers to the ten-cun chi. Six chi and four cun of the ten-cun chi is equivalent to eight chi of the eight-cun chi.) The *Xiao Erya: Guang Du Pian* states: "Kui is the distance covered by one step; double Kui is called Bu (step)." (*Kui* sounds like 'kui'). The *Sima Fa* states: "Six chi make one Bu." Zheng Shizi commented: Examining the systems of Yao, Shun, and the Xia Dynasty, a step was consistently six chi of the Xia Chi. The Shang Dynasty used 1.25 chi of the Xia Chi as its own chi, so it defined a step as five chi. The Zhou Dynasty used eight cun of the Xia Chi as its own chi, so it defined a step as eight chi. (Calculating with 1.25 chi as the base, multiplied by five, yields 6.25 chi of the Xia Chi. Calculating with eight cun as the base, multiplied by eight, yields 6.4 chi of the Xia Chi. Therefore, one step in the Shang Dynasty equaled 6.25 chi of the Xia Chi; one step in the Zhou Dynasty equaled 6.4 chi of the Xia Chi.) Currently, the copper rulers cast by the Baoyuan Bureau and kept by the Ministry of Works define five chi as one step. These current five chi are equivalent to 6.4 chi of the Xia Chi, or eight chi of the Zhou Chi. If the eight cun of the Xia Chi are evenly divided into ten cun, it becomes the Zhou Chi, which is the smallest. If the 1.25 chi of the Xia Chi are evenly divided into ten cun, it becomes the Shang Chi, which is the largest, and corresponds to the carpenter's square ruler used today. Passed down from Lu Ban through generations until the Tang Dynasty, where it was called the Large Chi, and continued to be used until now as the Jin Chi or Yingzao Chi, this ruler is essentially the Chi of King Tang of Yin. Removing two cun from it yields the Chi of Yu of Xia. Removing two cun from the Chi of Yu of Xia yields the Chi of King Wu of Zhou. Thus, a single carpenter's square ruler encompasses the systems of the Three Dynasties, making it self-evident without needing to count millet grains. Furthermore, from the Yellow Emperor to Shun and Yu, the systems were inherited without alteration; only with the Yin and Zhou dynasties did changes in orthodoxy and calendar start occur, leading to the introduction of adjustments in measurements. Therefore, we can infer that the acupoints in the *Huangdi Neijing Lingshu* (Yellow Emperor's Classic of Acupuncture), the unification of laws and measures by Shun, and the bodily proportions of Yu were all consistent with the Xia Chi.

It is further stated: Qibo's mention of an "eight-chi tall man" aligns with the *Rites of Zhou*'s statement that "human height is eight chi." This indicates that from the Yellow Emperor down to the late Zhou period, spanning thousands of years, human stature and measurement standards remained unchanged. This likely referred to the height of exceptionally tall men, not the average person. Hence, the Yellow Emperor asked Bo Gao about the average height, which was seven chi and five cun. This is corroborated by the *Waitai Miyao*, which also records seven chi and five cun. Tao Hongjing of the Liang Dynasty, in his preface to the *Bencao*, exclusively used the millet-counting method. Sun Simiao followed suit, using the Ancient Xia Chi in his texts and cross-referencing it with the *Sima Fa*'s definition of "six chi as one step." His meticulous approach far exceeded that of ordinary physicians. However, Sun Simiao claimed that the Ancient Xia Chi was the small eight-cun ruler used in Jianghuai, Wu, and Yue regions, equivalent to eight cun of the Tang Chi. The *Tang Huiyao* records: "In the fourth year of Wude (621 AD) under Emperor Gaozu of Tang, Kaiyuan Tongbao coins were issued, with a diameter of eight fen, corresponding to eight fen of the Tang Chi." If one coin has a diameter of eight fen, ten coins lined up have a diameter of eight cun, which constitutes one chi of the Ancient Xia Chi mentioned by Sun. Kaiyuan Tongbao coins still exist today; thus, by examining the coins, the size of the chi can be determined. In recent times, physicians adopted the "same-body inch" method, abandoning archaeological research. Fortunately, Sun Simiao's prescriptions and the *Tang Huiyao* provide evidence. The standard height for ordinary people should be based on seven chi and five cun of the millet chi. Cao Jiao, being very tall at nine chi, was above average; Yan Zi, being short at six chi, was below average. Taking the average of these two extremes yields seven chi and five cun. Therefore, Confucius and Xunzi stated that a body of seven chi represents the average person. Seven chi and five cun of the millet chi is equivalent to six chi of the current carpenter's square ruler. The "eight chi" mentioned in the *Suwen* and *Rites of Zhou* refers to eight chi of the millet chi, which equals 6.4 chi of the current carpenter's square ruler, representing the stature of giants. Thus, the *Suwen* contains two theories: eight chi and seven chi five cun. Vulgar people, ignorant of the differences between ancient and modern scales, absurdly claim that human constitutions differ between ancient and modern times.