Mountain 6 of the twenty-four mountains (luopan) is Yin, the Earthly Branch also carried in the Chinese zodiac as the Tiger, occupying position NE3, northeast sector, 52.5 to 67.5 degrees. Yin is a yang branch whose fixed agent is Wood, and it is a growth branch: within it the sexagenary system stores three hidden stems, Jia (yang Wood) as its principal qi, with Bing (yang Fire) and Wu (yang Earth) carried inside it. In the trine groupings that gather the twelve branches into four three-branch sets, one for each of the four elemental phases, Yin functions as the branch that opens the Fire trine.
Twelve of the ring's twenty-four positions are branches rather than stems or trigrams, and they are the only ring of the three that also carries a fixed two-hour span of the traditional Chinese day, Yin's own double-hour, and a solar month, so a branch mountain names a direction, a time of day and a season in one and the same character, a triple duty neither the stem ring nor the trigram positions carry. Because ten stems and twelve branches do not share a common factor larger than two, a given stem does not return to a given branch until the combination has cycled sixty times, the sexagenary count (jiazi) that names years, months, days and hours across the traditional Chinese calendar; a mountain's own stem or branch name is therefore also, in a different context entirely, a recurring building block of that sixty-term cycle.