How is Gengri calculated?

Gengri is a term used to record time, and a Gengri is ten days.

In ancient China, time was recorded through the combination of heavenly stems and earthly branches. The number of heavenly stems is 65,438+00, namely, A, B, C, D, E, G, Xin, Ren and Gui, so there is a Geng Day every 65,438+00 days.

"The third watch" refers to the three characters of "Geng" from the summer solstice, the third watch is the first day of lodging, the fourth watch is the first day of lodging, and the first watch after beginning of autumn is the first day of lodging for the last time.

The first day and the last day are 10, and the days in between are not fixed. There are four Geng days between the summer solstice and beginning of autumn, with an average of 10 days; There are five Geng days with an average of 20 days.

According to the ancient calendar of China, it is now determined that the first day of the first autumn is the third Geng day from summer to the future; The first day of the Mid-Autumn Festival is the fourth Geng Day from summer to the future; The last day is the first watch after beginning of autumn.