How to record and calculate ancient days?

Using heavenly stems and earthly branches to calculate the order of year, month and day is a method adopted by our people for more than 2000 years. The heavenly stems are A, B, C, D, E, Ji, Ke, Xin, Ren and Gui, and the earthly branches are Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai. Why use dry branches to calculate the year, month and day? In ancient times, day and night were not calculated according to 24 hours, but according to 12 hours, and one hour was two hours. Starting from midnight, it is counted as children's time, followed by clown time and Yin Shi time, with noon in the middle of the sun. In ancient times, the days were counted by dry branches, which circulated once every 60 days, and the months were counted by dry branches in the summer calendar, which circulated once every 5 years. The first month is Yin Shi, and the twelfth month is ugly, which is called Jian Yue. A leap month is an extra month, and no month can be created. These algorithms are old habits, and they are basically not used now. It is also called "Year Time", which records the chronological order with Jiazi and Night Ugliness, and it is also called changing armor once every 60 years. After liberation, the international Gregorian calendar has been adopted, and at the same time, the year order of the summer calendar is still represented by branches. This method of making the chronology of cadres and branches quickly is convenient to check the historical years and conforms to the habits of Chinese people.