Why do twelve satellites have duplicates?

Twelve satellites (twelve digits) represent twelve days of construction, division, filling, leveling, determination, persistence, breaking, danger, success, closing, opening and closing. For example, in the next year, the child will be built, the ugliness will be removed, and the number will go; Ugly year, build ugliness, divide yin.

Twelve satellites are built twice a month, namely, the first lunar month, the second lunar month, the second lunar month, the third lunar month, and so on. The first month is, so two of the six cloudy days (Jiayin, Bingyin, Wuyin, Gengyin and Nonyin) must meet the sword. February is, so two of the six dates (Yi Mao, Ding Mao, Ji Mao, Xin Mao and Gui Mao) must meet the sword, otherwise it will be wrong.

Every festival (beginning of spring, Vitex negundo, Qingming, Long Summer, Mango, Xiaoshu, beginning of autumn, Bailu, Cold Dew, beginning of winter, Heavy Snow and Slight Cold) is as important as the two constellations of the previous day, so as to ensure that the first and second days of this month are the same as the lunar branch.