You must recite the formula from the beginning of the month.

From the first day of the month, I must recite the formula: the first year of Jiaxu is the first, and the second year of Geng is the first. Bing Xin will definitely go to Geng, and Ding is just downstream. If you ask me where to send it. Jain is good at pursuing.

When it comes to the year when the sky is dry, it is C in the first month, D in February, and the year after E in March. Ding is downstream, that is, the year when he met Ding or Ren, and the first month began with Ren. You ask me where to send it, which is easy to pursue above the good news. That is to say, in the year of Wuzi or Guiwei, the earthly branch of the first month was Jiayin, because the earthly branch of the first month was Yin Yin.

From a certain day of the month

There are twelve months in a year with an average of 365 days. Regardless of the fact that leap years have one more day than normal years, we can find that the relationship between days and months is not so clear only considering 365 days.

We calculate 30 days in a month, divide 365 by 30, and the number is more than 12. That is to say, even if there are only 365 days in a year and 30 days in a month, it is impossible to distribute these 365 days evenly in 12 months of a year, and there are always 5 days that suddenly appear. Heavenly stems and earthly branches's group takes sixty as a rotation cycle, sixty is twice as much as thirty, and five times twelve is sixty.

Even if there are only 365 days in a year, the extra 5 days will take 12 years to form a cycle. If we add leap years and different days in different months, the relationship between months and days will be more complicated.