Time and location
Local civil time must be interpreted in the correct historical timezone. A nearby city or a modern timezone rule can change the instant used for the chart.
BaZi transparency
Different inputs and conventions can produce different charts.
A result is not self-explanatory. Time zone, daylight-saving history, birth location, solar-term boundaries, late Zi Hour treatment, unknown time and school conventions can all matter.
Solar terms
Year and month pillars can change around Jie Qi boundaries. A versioned, signed solar-term dataset makes the chosen boundary auditable.
Conventions
Late Zi Hour, true-solar-time policy and treatment of unknown birth time are methodology decisions. Different schools are not automatically errors.
MyTongShu’s boundary
MyTongShu records the approved method, time basis and location resolution. Ambiguous or unsupported inputs fail safely for review rather than being silently guessed.