Mountain 15 of the twenty-four mountains (luopan) is Ding, one of the eight Heavenly Stems placed on the ring, occupying position S3, south sector, 187.5 to 202.5 degrees. Ding is Yin Fire, and its classic image is the contained flame, the candle, lamp or hearth fire. In Four Pillars astrology, where a person's chart is read from the stem and branch of the year, month, day and hour, a Ding Day Master, the stem governing the day of birth, is described as thoughtful, sensitive and quietly influential, though it may flicker with moods or burn low when unsupported.
Ten Heavenly Stems exist in the full sexagenary system, one yang and one yin stem for each of the five elemental phases, but only eight reach the compass ring: the pair for Earth, Wu and Ji, is withheld from the perimeter and reserved to the centre, following the same five-phase logic recorded elsewhere in this atlas under which Earth's own direction is the pivot rather than any one of the eight compass points. 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.