Nayin, English is At the sound, refers to a method of obtaining numbers that was widely used in ancient Chinese mathematical predictions. Its corresponding mathematics has been clearly stipulated by Nayin in the Sixty Years. Its basic meaning is still explained in terms of "five elements".
The "yin" of "Nayin" is the five tones determined by the ancient Chinese people based on different scales. The five tones are a highly abstract summary of the sound patterns of nature by the ancients.
Take "Jia Zi, Yi Chou, and there is gold in the sea" as an example. The mathematician explained it like this: Four, subtract it from forty-nine, leaving fifteen. Remove ten and leave five unused. Five is Gongyin, which belongs to earth, and earth can produce metal. This shows that "Jia Zi Yi Chou" is related to "Gold". This correlation is derived from the five elements.
And because Zi belongs to water, is a lake, and is a place with strong water, and metal dies in water, and the tomb is in Chou, water is prosperous and metal dies, so it is called Jia Zi Yi Chou in the sea. That is to say, the reason why "Jia Zi and Yi Chou" are gold in the "sea" rather than gold in other places is because "Zi" is related to "water", and of course there is a lot of water in the sea.
Also, "ugly" is soil, which is the place where "gold" is buried and carried. When metal reaches water, it will sink to the soil at the bottom of the water, so the principle of "a piece of metal is found in a piece of metal, a piece of metal is found in a piece of metal".
Extended information
Earthly Branches Nayin
The five elements of Nayin are assigned to the earthly branches, which is different from the conventional earthy branches and five elements system. The twelve chen and five tones of the earthly branches are as follows:
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The palace number one belongs to earth, which is the king and the body; the son is the yang palace, and the noon palace is the yin palace;
the sign number three is fire, and it is the ancestral temple and ancestors; Chou , Yin is the yang sign, Wei and Shen are the yin sign;
The number of feathers is five, which belongs to water, which is the realm and wife's wealth; Mao is the yang feather, and You is the yin feather;
The number of quotient is seven, it belongs to metal, it is officials and servants, it is descendants; Chen is Yang Shang, Xu is Yin Shang;
The number of horns is nine, it belongs to wood, it is illness, it is death; Si is Yang angle , Hai is the Yin angle.
From Zi to Si, they are all born from the law of yin, so they are yang; from Wu to Hai, they are all born from the law of yang, so they are yin.
Baidu Encyclopedia—Nayin