Xu is the eleventh of the twelve Earthly Branches (dizhi). Its zodiac animal is the Dog, its element is Earth, its direction is west-northwest, and its double-hour runs from 7 to 9 pm, the early evening. As one of the twelve branches it combines with the ten Heavenly Stems to form the sexagenary cycle of sixty that numbers years, months, days, and double-hours. The branch names the eleventh animal of the twelve-year cycle and the corresponding month and double-hour, carrying the Dog's loyal and watchful associations in the almanac. These are the conventions of the Chinese calendrical and cosmological tradition, in which the twelve branches order the twelve-year animal cycle, the months, and the twelve two-hour periods into which the day is divided.
Xu is the eleventh Earthly Branch, corresponding to the Dog, and to the double hour from 7 pm to 9 pm, early evening. Its dominant hidden stem is Wu, giving it the Earth phase, with Xin and Ding present as secondary hidden stems. Xu is a Yang-polarity branch, pairing only with Jia, Bing, Wu, Geng or Ren within the sexagenary cycle, and it governs the ninth lunar month and the compound northwest direction. In BaZi astrology a chart with Xu prominent is read through the Dog's traditional associations of loyalty, honesty and a strong sense of justice, sometimes to the point of an inflexible moral rigidity that the tradition treats as the same trait's shadow side. The Dog also appears, alongside the other eleven branch animals, in the widely repeated origin legend of a race called by the Jade Emperor to fix the order of the zodiac, a folk tale first recorded relatively late and not part of the branch system's own ancient textual history.