What is the eight characters? What's the use?

It is the time of birth, including year, month and day. Use heavenly stems and earthly branches to indicate your birth time. A * * * eight words. So it's called eight characters.

Its purpose is to understand everyone's life trajectory from birth to death. Know when your luck is bad. When is luck? Find out whether your marriage is good or bad. Rich or poor. Character and temper. Physical illness, etc. . .