What are 99 songs? How to calculate?

The solar terms of 1999 are as follows:

If you don't do this in 1929,

Walking on the ice in 3949,

Looking at the willows by the river,

Seven or nine rivers are open,

Eight or nine Yan came,

99 plus 19,

Cows are plowing the fields everywhere.

Count nine customs:

The written record of the custom of "counting nine" was first seen in the Chronicle of Jingchu Times written by Liang Chaozong in the Southern and Northern Dynasties in 550 AD, with a history of 1445 years. It is recorded in the book that "the number of winter solstice days is 99,81day is the end of cold".

Winter Jiujiu songs are spread all over the country, but the lyrics are slightly different. People all over the country have compiled various proverbs, ballads and fluency according to different climatic conditions, scenery characteristics, agricultural phenology and customs.