The 60-year cycle that keeps time in Chinese cosmology.
Ten Heavenly Stems (天干) pair with twelve Earthly Branches (地支) to produce sixty unique combinations — the jiazi (甲子) cycle. One cycle covers sixty years, sixty days, or sixty two-hour watches, depending on context. Each branch is also mapped to one of the twelve zodiac animals. Together, the stems and branches are the oldest continuously-used calendar system on Earth.
Beyond pairing with stems, branches interact with each other through punishments, conflicts, and affinities. These relationships shape the reading of a chart in Wen Wang Gua and BaZi.