Local civil time
The wall-clock time recorded at the birthplace.
BaZi method · evidence guide
Why BaZi calculators disagree
Time zones, solar terms, true solar time, and Four Pillars boundaries
Two BaZi calculators can receive what looks like the same clock input and still disagree because the hidden assumptions around that clock may differ. Sibyl exposes those assumptions instead of pretending every disagreement has one universal answer.
One birth record, four time frames
Birth instant UTC
The unambiguous global instant after civil-time resolution.
Local true-solar wall time
A longitude-adjusted local wall clock used by Sibyl's versioned true-solar convention.
Solar-term instant UTC
The absolute astronomical instant used by the approved year and month boundary layer.
Do not compare different kinds of clocks
Sibyl compares the resolved birth instant in UTC with the solar-term instant in UTC for year and month boundaries. A longitude-adjusted true-solar wall clock is not compared directly with a UTC solar-term instant.
A local clock time can be invalid or ambiguous
An invalid calendar date fails. A DST gap is a local time that never occurred and must fail rather than silently slide forward. A DST overlap can describe two different global instants, so Sibyl exposes the earlier and later occurrence for explicit selection.
Historical timezone data is part of the evidence
Historical offsets can differ from today's offset. Sibyl keeps runtime timezone provenance visible and does not pretend the browser or Node runtime represents a specific tzdb release when that provenance cannot be established.
True solar time changes a local wall clock, not the global instant
Longitude correction can move the displayed true-solar wall time across civil midnight. That can affect the approved local day/hour convention while the original civil record and resolved global instant remain distinct evidence.
Li Chun and monthly boundaries are absolute instants
The same Li Chun instant applies globally. Shanghai, Tokyo, New York, and London display different local clock times for that event, but the underlying instant is the same. Sibyl's year and month boundary logic works from that global instant.
Precision can force a non-answer
Inside Sibyl's ±5-minute boundary-sensitive window, insufficient source precision returns HIGH_PRECISION_REVIEW_REQUIRED. Definite Four Pillars and derived fields are withheld instead of guessing which side of the boundary applies.
Day and hour conventions must be named
Sibyl currently uses its frozen sect-2 pipeline: the Zi double-hour spans 23:00–01:00 while day rollover follows the approved civil / true-solar midnight pipeline. Another calculator can differ if it uses another rollover convention.
A practical comparison checklist
- Birthplace and IANA timezone
- DST gap and overlap handling
- Historical offset provenance
- True-solar mode and longitude
- Li Chun and monthly solar-term instants
- Boundary precision policy
- Zi-hour and day-rollover convention
- Method and adapter version
What this page does not decide
This page explains deterministic time and boundary behavior already implemented in Sibyl. It does not calculate Day Master strength, chart structure, Useful God, favourable elements, luck cycles, health, wealth, relationship outcomes, or a universal BaZi school consensus.