When heavenly stems and earthly branches Chronology is used, the year, month, day and time are all expressed by heavenly stems and earthly branches. For example, we are familiar with the Sino-Japanese War. A stands for heavenly stems, which means what we call A, B, C and D, and noon is earthly branches, which means that the earthly branches of a day are expressed by the chronology of earthly branches, such as Jiazi Day, and earthly branches are "sons".
This is a fortune-telling term.
Reference:/blog/static/12153653820091139251500/