How did the ancients discover heavenly stems and earthly branches and the principle of eight-character calculus?

Date of birth is date of birth. It doesn't have to be accurate to the second, but it should be accurate to the hour.

You only said the year, month and day, but you didn't report all the people.

Heavenly stems and earthly branches's calendar is Jiazi's calendar. There are ten days of work: A, B, C, D, E, G, Xin, Ren and Gui.

There are 12 earthly branches: Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai. These twelve are the zodiac signs. The child is a mouse, ugly is a cow, and so on, and Hai is a pig.

Arrange the trunk with the branches, with the trunk in front, the branches behind, the trunk from A and the branches from Zi.

The first year is the year of Jiazi, the second year is the year of ugliness, and then the year of Bingyin. By analogy, a 60-year cycle is a nail. That's what the ancients did, counting every 60 years! !

As for your eight characters and five elements, I can add them all up for you! !