For example, let’s talk about the 21st century 90s. How about ancient times?

The 21st century 90s that we are talking about now is actually a term that only exists in the AD era. The AD era is also called the AD era, abbreviated as "AD" or "AD". The Christian calendar is the Christian calendar. In 525 AD, the Roman monk Dionysius identified the birth year of Jesus as the first year of the Christian era.

In ancient China, the main methods used were the chronology of the stems and branches and the chronology of the emperor's years. There is no corresponding explanation for the two. Let me explain to you the chronology of the years and the chronology of the stems and branches.

1. Calendar of years with era names. Chinese emperors have had their own era names since Emperor Wu of the Han Dynasty, and their era names have been used as a method of chronology. For example, the 20th year of Kangxi (AD 1681).

2. Stem and branch chronology

It is a traditional Chinese chronology method. It is composed of ten heavenly stems (A, B, C, D, Wu, Ji, Geng, Xin, Ren, Gui) and the twelve earthly branches (Zi, Chou, Yin, Mao, Chen, Ji, Wu, Wei, Shen, You, Xu, Hai) are combined in turn. It started in Jiazi and ended in Guihai. A reincarnation takes 60 years, which is called sixty years.

It is also said that in 1681 AD, the 20th year of Kangxi, the year of chronology using the stems and branches was Xinyou. By combining the stems and branches with the emperor's year number, we can determine the specific year in history.

Hope it helps you again.