This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Joseph Needham's Science and Civilisation in China, in the volume covering mathematics and the sciences of the heavens and the earth, is the standard scholarly history of how the sexagenary cycle came to organize Chinese timekeeping, tracing the stem and branch system back through the Shang dynasty's own use of the sixty day cycle for naming days, centuries before the same paired sequence was extended to name years as well.
Needham's account documents the cycle as a genuine mathematical structure, ten stems and twelve branches advancing together rather than independently, whose least common multiple of sixty is the entire reason a full return to any one combination takes exactly sixty years, a property the system's own users have long understood and built ceremony around, the sixtieth birthday marking a complete cycle in traditional East Asian reckoning.
The history recorded here also traces how the five elements, themselves an older and separate Chinese cosmological scheme, were layered onto the ten heavenly stems relatively late, two stems to an element across two consecutive years, and how the twelve zodiac animals attached to the branches through a documented, though not perfectly settled, textual history rather than an origin as old as the stems and branches themselves.
An entry draws on this documented scholarly history for the cycle's own mechanics and chronology, keeping the plain historical fact, how the sixty year pattern actually works and where each of its parts came from, separate from the traditional divinatory readings a year's stem, branch and element combination is popularly given.