1929, I can't reach out; 3949, walking on ice and snow; 5969, look at the willows by the river; Seven or nine rivers open, eight or nine Yan comes, nine or nine cold tails, and spring blossoms.

This is similar to solar term song, and it is called "Counting Nine Songs".

1929, the weather was too cold to stretch out. In 3949, the ice and snow on the road had accumulated very thick. In May, 1969, the weather turned warm, with the breath of spring. Willows can be seen sprouting across the river bank, and the ice on the surface has melted in July, 1999. When the swallows came back in August 1999, they were already busy farming, and the farmland was full of cows.

That is to say, the formula of the weather. He counted the days ... one nine days, two nine days. . Different regions have different versions.