Formula · Astronomy and calendar
Ten stems and twelve branches allow 120 pairings, but only 60 satisfy both congruences at once; the other 60 cannot exist. 10 × 12 ÷ 2 = 60 is why the cycle is sixty long, not a hundred and twenty.
Number theory: Chinese remainder theorem with non-coprime moduli
Astronomy and calendar
This one is astronomy and calendar: verifiable against civil dates and solar-term tables.
Related: Five phases and stem-branch glossary · all formulas · tools
Where is this formula used?
It is the same entry listed on the method page, used in pages such as Five phases and stem-branch glossary; the link above shows it in context.
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This one is astronomy and calendar: verifiable against civil dates and solar-term tables.