What day is Unite Day?

Unitary day is a method of recording days in the old yellow calendar, which can be found in the perpetual calendar.

Geng Xin Shen Youli has two solutions:

First of all, it refers to the sky, with four words: Geng, Xin, Shen and You.

Secondly, it means that it must be the sun in Geng Shen and Xin You, and it will circulate every 60 days. Appears in hexagrams with a specific meaning.