How many days is the volt?

Er Fu this year is 10 days, and some years are 20 days. One volt and three volts fixed 10 days. I copied an article from my blog, you can have a look. This article is called: How to calculate the ups and downs, and tell you how to calculate the ups and downs. It's getting hotter and hotter, and it's the summer solstice in a blink of an eye. It suddenly occurred to me that it would fluctuate, but when would it fluctuate? I checked my calendar and said I was prone on July 20. I don't know how to calculate this. It is very simple to count nine days in winter. After beginning of winter, I counted one and nine every nine days, but I didn't know how to count them when it was in the dog days. Moreover, the annual accommodation time is not fixed, and the length of accommodation is different. It's really troublesome to look up the almanac calculation. I looked online, and there are so many things in this field. However, it is basically two sentences: "Three Geng in summer" and "Three Fu in autumn". It's easy to say, but it's really troublesome to calculate. The third Geng day from the summer solstice refers to the third Geng day from the summer solstice to the future. In ancient China, the "trunk-branch calendar" was popular, and 60 groups of different names were used to record dates with 10 heavenly stems and 12 earthly branches, which were recycled. The day with the word "Geng" is called "Geng Day". The word "Geng" in Geng Day is the seventh word in "A, B, C, D, E, Ji, G, Xin, Ren, Gui" 10 day, and it is repeated every 10 day. Starting from the summer solstice, according to the date of trunk, the third Geng day is the first, the fourth Geng day is the middle, and the 1 th Geng day after beginning of autumn is the last. In this way, one volt is ten days, three volts is ten days, but two volts is not necessarily, there are ten days and twenty days. This is going to use the second formula. Autumn is three days after beginning of autumn. Thus, when there are four Geng days between the summer solstice and the beginning of autumn, the middle part is 10 days, and when there are five Geng days, it is 20 days. In addition, the summer solstice (usually around June 2 1 day) takes less than 50 days to reach beginning of autumn (usually around August 7), so there will be no six-watch day. It seems that the emergence of Gengri will affect the length of the first half sooner or later, so there will be 30 days in some years and 40 days in some years. What a bother. However, how to calculate Gengri is even more troublesome. There seems to be no way to calculate. Now push back day by day. Anyway, every 60 days, as long as you remember one day, you can push forward and push back. It is said that fortune tellers can remember dates for many years, which is really amazing. But now no one remembers. Anyway, it's very convenient to check. Why do you remember him? I just don't know when this calendar year started. By the way, there is an interesting and practical song "Summer Solstice" that has been on fire for nine days. "Summer Nine Songs": The summer solstice is in the top nine, and the feather fan is in hand; In 29 18, I took off my crown and put on a scarf; On March 27, I went out to sweat; 4936, sweating all over; In 5945, autumn was like a tiger; 6954, enter the temple to enjoy the cool; 7963, touching the sheets at the bedside; 8972, looking for a quilt in the middle of the night; 998 1, open the cupboard to get cotton-padded clothes. The ancients in China were really powerful. I admire them.