Method 1: year by year method. Count the years according to the years of the prince's reign.

Method 2: the method of years and years. Emperor Wu of the Han Dynasty began to have a title. Since then, every emperor has to change the throne and mark the year with the year number.

Method 3: chronology of trunk and branch.

Method 4: Count as both a stem and a branch. When the year is numbered, the emperor's year is put in front, and the cadres and branches are listed behind.