How is the 99 solar term calculated?

1 winter 99: from the winter solstice, every nine days is nine days, * * * 998 1 day; 2 Summer 99: From the summer solstice, every nine days is nine days, * * * 998 1 day; Three volts: from summer to the future (excluding summer solstice), the third Geng day is the first volt, the fourth Geng day is the middle volt, and the first Geng day after beginning of autumn (excluding beginning of autumn day) is the last volt; 4 plum entry: the first third day from the date of awning; 5. Plum blossom: the first unfinished day from summer; 6 Spring Club: the fifth May Day in beginning of spring; 7 Autumn Club: the fifth May Day in beginning of autumn; In addition, there are dragons and dragons, Long Rain, Three Points and Hua Xinfeng.