What is the meaning of "Twelve Laws" in China's traditional music terminology?

Twelve laws are generally divided into six laws and six laws. Six methods (also known as "Yang method") are odd methods such as Huang Zhong, Tai Qun, Gu Xi, Yan Bin, Yi Ze and Bushe, and six methods (also known as "Yin method") are even methods such as Lu Da, Jia Zhong, Zhong Lu, Lin Zhong, Nan Lu and Ying Zhong. Although the complete deduction method of the Twelve Laws appeared in the literature at the end of the Warring States Period, the Twelve Laws had been applied to music practice in the Western Zhou Dynasty or even earlier, and served as the theoretical basis for casting chimes after the Spring and Autumn Period.

According to "Mandarin? "Zhou Xiayu" records that in 522 BC, when King Jing of Zhou planned to cast a bell instead of shooting it, he asked the pigeons in Lingzhou. Answer to the Pigeon in Lingzhou already contains a complete set of twelve dharma names, which is the earliest record of twelve dharma names in known ancient literature. The inscriptions on chimes unearthed in the middle and late Western Zhou Dynasty also confirmed the above viewpoint.