What does eight characters mean?

Birthday, or eight characters, is actually another way of saying the four pillars of Zhouyi. Four pillars refer to the time when a person was born, that is, year, month, day and hour. When people use "heavenly stem" and "earthly branch" to represent year, month, day and hour respectively, such as Jiazi Year, Shen Bingyue, Guichou Day and Renyin Time, it contains the basic state of celestial movement when a person is born. There are two words in each column and eight characters in four columns, so fortune telling is also called "measuring eight characters" According to the relationship between yin and yang attributes and the five elements of heaven and earth, it is inferred that human body is responsible and blessed. However, what I want to talk about here is not how to "measure eight characters", but how to calculate eight characters. In order to get the correct time of birth, the sundial is the most accurate measurement during the day. When the clock time is the artificial average time and the regional standard, it is necessary to calculate the "apparent solar time difference" according to the solar terms (ecliptic) and the "local longitude time difference" according to the place of birth, so as to get the real astronomical birth time. In the eight characters, the annual and daily branches are continuous and true; The branch of month and time is calculated according to the branch of year and day, which can be said to be virtual.