How many days is a Geng?

One Geng is not fixed. In ancient China, time was recorded through the combination of heavenly stems and earthly branches. The number of heavenly stems is 10, which is A, B, C, D, E, Ji, G, Xin, Ren and Gui, and the number of earthly branches is 12, which is Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You and Xi. Match heavenly stems and earthly branches, and you will get Jia Zi, Yi Chou, Bing Yin and Ding Mao. Mating 60 times, so it is called 60 flowers.

"Three Geng" is to meet three "Geng" characters, and it will be the first time on the third Geng Day. Because the number of heavenly stems is 10, there is a Geng Day every 10 day, such as Geng Zi Day, Geng Yin Day and Chen Geng Day. 365 days a year is not an integer multiple of 10. One day this year is Geng Day, and next year is not necessarily Geng Day. Due to the uncertainty of Geng Day, the date of stay is different every year.