What does Hou Jia mean to Xian Geng in Melody Enlightenment?

I ching: "the first three days a, the last three days a", a is the first day of dry weather, and the last three days after a are auspicious days.

The Book of Changes-Xun: "Three days after Geng, three days after Geng, Ji." The third day of Geng Xu refers to three days before Geng Tian, which is also an auspicious day.

Because the last three days of A are Ding, the first three days of Geng are Ding, and the last one is Geng Shou.