Traditional Culture Encyclopedia - Lucky day inquiry - What do "Gu Erdan" and "Shang Huan" mean in genealogy or ancient books?

What do "Gu Erdan" and "Shang Huan" mean in genealogy or ancient books?

Gudan:

In ancient times, when the grain harvest was the best day, so "grain" meant "good luck", so it was called "grain harvest", which was the general name of good days.

Shang Huan:

Sheung Wan is on the first day to the tenth day of each month, Sheung Wan is on the 11th to 20th of each month, and Sheung Wan is on the 20th to 30th of each month.