Second Difficulty

The pulse has the designations "cun" and "chi." Why is this?

Answer: The so-called "cun" and "chi" are the most important meeting points of the pulse. From the Guan region to the Chi region is the area of the Chi pulse, which is governed by yin; from the Guan region to the Yuji (thenar eminence) is the area of the Cun pulse, which is governed by yang. Therefore, a portion is taken from the Cun region and called Chi, and a portion is taken from the Chi region and called Cun. Thus, the yin pulse receives one cun within the Chi, and the yang pulse receives nine fen within the Cun. The Cun and Chi together begin and end at one cun and nine fen, and for this reason they are named "cun" and "chi."