South-southeast, at 157.5 degrees, falls on the boundary between the mountain Si, the branch of the snake, and the mountain Bing, a heavenly stem lying just east of due south.
The luopan divides the horizon into twenty-four mountains of fifteen degrees, drawn from the twelve earthly branches, eight of the ten heavenly stems, and the four trigrams that occupy the corners. The European compass rose divides it by repeated halving into eight, sixteen and thirty-two points. The two schemes meet at eight places and diverge everywhere else, and each secondary point of the sixteen-point rose lands on a seam between two mountains.
Due south itself is the mountain Wu, the branch of the horse, and it carries more weight in Chinese orientation than any other bearing, since south is the direction a ruler faces and the direction a hall is conventionally oriented toward. Bing and Ding, the two stems flanking Wu, therefore sit in the most closely watched arc of the whole ring, and the fifteen-degree distinction between them and the horse is not a technicality in the compass schools.
Si, the snake, is the double hour from nine to eleven in the morning, and in the cycle of months it belongs to the fourth. As with every mountain, the character carries a direction, an hour and a season together, which is what allows a luopan reading to be cross-checked against a date.