The eight-character pure yin is generally not specific when to be born, but is judged by a person's eight-character year column, moon column, sun column and time column. If all four pillars correspond to Yin, it is pure Yin in eight characters.
For example, on the 10th, B, D, I, Xin and Gui are Yin, and ugly, hairy and defensive, especially pure Yin among the twelve branches. Therefore, if a person's four pillars all fall on these pure Yin heavenly stems and earthly branches, then this person is a pure Yin life.