A clock time needs a place and a date
“Three in the afternoon” only identifies an instant when paired with the time zone and daylight-saving rules in effect on that date. Today’s UTC offset may differ from the historical offset at birth. Mainland China also observed daylight saving in some years.
Wenbu accepts IANA zones such as Asia/Shanghai and America/New_York. Do not substitute your current device zone for the zone where you were born, especially after moving countries.
Some clock times are missing or repeated
A spring clock change can skip a time; an autumn change can repeat it. Wenbu rejects these ambiguous or nonexistent inputs instead of silently picking an instant. Resolve the recorded time and supply an explicit UTC offset when necessary.
In New York, 02:30 on March 10, 2024 did not occur on the local civil clock. At the autumn transition, 01:30 on November 3, 2024 has two possible offsets. A birth record or other reliable historical information is needed to choose.
What does solar-time correction change?
Local mean solar time follows longitude, at approximately four minutes per degree. Apparent solar time also accounts for the equation of time. Longitude, a time-zone meridian and daylight saving are different inputs.
Wenbu offers an approximate apparent-solar-time correction, requires a longitude and shows the correction in minutes. It is not a high-precision ephemeris. Near a pillar boundary, compare the corrected and uncorrected results rather than treating an approximate correction as definitive.
Save the convention with the result
The default day boundary is midnight; a 23:00 Zi boundary is also available. In the library’s midnight convention, a late-Zi day pillar stays on the civil day while the hour stem advances. The chart discloses that choice.
Year and month pillars follow absolute solar-term boundaries. Day and hour pillars use the selected local clock. Exports preserve the settings so a discrepancy with another calculator can be investigated rather than explained away.
Sources & further reading
Hong Kong Observatory · Gregorian–Lunar conversion tables ↗US Naval Observatory · The equation of time ↗lunar-typescript · calculation source and examples ↗Traditional interpretations are not established predictions. See the source notes for context.