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THE SHORT ANSWER
A recorded clock time identifies an instant only after its date and historical time zone are known. Solar time is a separate calculation convention, combining a longitude adjustment with the equation of time. Wenbu applies its approximate correction to the local clock used for day and hour pillars; year and month transitions still use the original instant.
- Resolve the recorded time zone before considering solar time. A solar-time switch cannot repair an incorrect date, DST assumption or UTC offset.
- Use positive longitude east of Greenwich and negative longitude west. Wenbu adds 4 × longitude − UTC offset in minutes + equation of time.
- Near a day or hour boundary, retain both sets of conventions and results. An approximate correction cannot remove uncertainty in the birth record.
Gregorian date, local clock time and precision
Birthplace IANA zone and offset on that date
On/off, longitude, correction and formula
Midnight or 23:00; late-Zi hour-stem convention
Four cards identify the information needed to check the birth record, historical time zone, solar-time convention, and day/hour boundaries. Use them to locate the layer behind a disagreement. The full table below adds year/month transitions and common mistakes; the worked example then preserves the original instant alongside the correction.
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’s BaZi calculator 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.
Find the layer that differs between two charts
| Layer | Information to compare | A common mistake |
|---|---|---|
| Birth record | Gregorian date, local clock time and precision | Entering a lunar date in a Gregorian field |
| Historical time zone | Birthplace IANA zone and offset on that date | Using the current residence or subtracting DST twice |
| Solar-time convention | On/off, longitude, correction and formula | Reversing longitude or confusing it with equation of time |
| Day and hour boundaries | Midnight or 23:00; late-Zi hour-stem convention | Comparing interpretation before checking different day pillars |
| Year and month transitions | The same instant and solar-term boundary | Applying the local solar correction to the transition again |
On a small screen, scroll the table sideways.
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.
Compare disagreeing charts one setting at a time
Check the Gregorian date and local clock time first, then the time zone and daylight-saving treatment. Next compare solar-term boundaries, the day boundary and solar-time correction. Change one setting at a time and note which pillar changes.
For example: “The year and month pillars agree, but the day pillar differs for a time near 23:00. Please compare the day-boundary rules first.” Use clearly labeled example details when you only need to demonstrate the issue.
Work through a solar-time adjustment
Assume a record of December 23, 2005 at 08:37 in Asia/Shanghai and a teaching longitude of 121.5° east. This is a specified coordinate, not a claim that every Shanghai birthplace has that longitude. The equation of time uses Wenbu’s current approximate formula.
Resolve the historical offset: UTC+08:00, or +480 minutes. The original instant is 00:37 UTC. Keep that instant for year and month solar-term comparisons.
Calculate the longitude component: 121.5 × 4 − 480 = +6 minutes. The chosen point is 1.5° east of the 120° standard meridian, making local mean solar time six minutes ahead.
Add the formula’s equation-of-time value for the date, approximately +1.3 minutes. The total adjustment is about +7.3 minutes, producing approximately 08:44 apparent solar time. Displayed seconds do not turn the approximation into a precise observation.
Check the relevant boundaries. Both 08:37 and approximately 08:44 remain in the Chen hour and on the same day. The example therefore retains Yi You / Wu Zi / Xin Si / Ren Chen. Applying a correction does not necessarily change a pillar.
Save the original 08:37, the zone, 121.5° longitude, the enabled setting and the +7.3-minute correction. Do not enter 08:44 as the new original time with correction still enabled; that would apply the adjustment twice.
A reproducible chart preserves the recorded time and each transformation. The useful questions are whether a boundary was crossed and whether the birth record is precise enough, not how many decimal places the software displays.
Key terms
- UTC offset
- The difference between a local clock and UTC on the relevant date; today’s offset is not necessarily the historical one.
- Local mean solar time
- Mean solar time expressed at a particular longitude, changing by about four minutes per degree.
- Equation of time
- Here, apparent minus mean solar time: a positive value means apparent solar time is ahead.
Common questions
Should an overseas birth be entered in Beijing time?
Enter the recorded local time and birthplace time zone. Wenbu internally uses fixed UTC+08:00 for the same instant when checking solar terms. Its day and hour calculation follows the selected local-clock convention. Converting the input yourself and retaining the birthplace zone would misidentify the instant.
Should I subtract daylight saving after choosing an IANA zone?
Usually not: the time-zone library resolves the offset for the date. Wenbu rejects skipped or ambiguous local times during clock changes. Clarify the record and provide the intended offset rather than choosing one arbitrarily.
Is apparent solar time always the correct choice?
It is a different convention with an astronomical definition. That definition does not establish which interpretive school makes more valid claims. State the convention first and compare results near a boundary.
Sources and their scope
Defines apparent time, mean time and their difference; example values come from Wenbu’s approximation, not an observatory ephemeris.
Explains the location-based database of historical UTC offsets and daylight-saving rules.
Documents the formula, signs, rejection of ambiguous inputs and separate pillar handling; the +7.3-minute example was recalculated.
Explains solar terms as ecliptic-longitude boundaries, distinct from a local-clock or longitude adjustment.
Further reading; not validation of real-world predictions.
Further reading; not validation of real-world predictions.
Traditional interpretations are not established predictions. See the source notes for context.
Read this guide with your agent
Get the complete text, diagram descriptions and sources in an open format. These files contain public knowledge only.
ADDITIONAL PRACTICE · 2026-11-11
A repeated 1:30 a.m. has two possible UTC instants
Copy the birthplace, local date and clock reading first. If the clock reading occurred twice that day, keep two rows with different UTC offsets. In New York on November 3, 2024, 1:30 a.m. can mean 05:30 UTC or 06:30 UTC. Both requests in this exercise return the same four pillars. Leave the offset unresolved until a record can distinguish the two instants.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
- Keep the civil clock reading apart from its UTC candidate.
- Save one receipt for each offset instead of overwriting the first one.
- Matching pillars do not identify which instant the note describes.
One clock reading, two records
- 01Copy
Keep the original local date and 1:30 a.m.
- 02Fork
Create a row for -04:00 and another for -05:00.
- 03Check
Compare 05:30 UTC and 06:30 UTC with the two receipts.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
Put the two instants on paper
Imagine a fictional note with only the city, November 3, 2024 and 1:30 a.m. Write that down before trying any calculator. New York's clock moved back that morning. The time zone names the set of rules for the city, but the note does not say whether it refers to the first or second occurrence of the hour.
On the first row use the offset -04:00. Adding four hours to 01:30 gives 05:30 UTC. On the second row use -05:00. Adding five hours gives 06:30 UTC. Both are on November 3 in this example. When you check another reading closer to midnight, verify the UTC calendar date as well as the hour.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
Read the result without choosing a birth time
Send the date, local reading and America/New_York to the Wenbu calculator. The example is rejected with HTTP 422 and a message about an ambiguous or nonexistent time. Next, use the two explicit offsets in separate checks. The receipts give different UTC instants. Leave every other setting in place so the offset is the only changed input.
Both receipts return Jia Chen, Jia Xu, Xin Wei and Ji Chou. Write that next to the two instants without merging the rows. A birth record that names the applicable offset, or another reliable record of the absolute time, could resolve the question. Agreement between these computed pillar values gives no such evidence about the recorded time.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
| Input | Expected receipt | How to record it |
|---|---|---|
| America/New_York | 422 for the ambiguous clock reading | Offset unresolved |
| -04:00 | 05:30 UTC | Candidate A |
| -05:00 | 06:30 UTC | Candidate B |
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
Hypothetical practice with an ambiguous note
This is a fictional timing record for checking the calculator. It is not a person's birth data.
- Copy the note and leave the offset unknown in the original record.
- Create two comparison rows and change only the offset.
- Check the UTC values. They are an hour apart, even though the four pillar values agree.
Keep both rows and leave space for the source of any later decision.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
Questions you may have
Should I choose standard time when the input is ambiguous?
Keep both candidates unless you have a record that identifies the occurrence. A default offset would conceal the missing detail.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
Do I need both rows if the pillars match?
Yes. Each row records a different possible instant. Another calculation that uses absolute time can still require that distinction.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
Terms in this guide
- Repeated clock time
- The same local clock label occurs at two actual instants during a fall-back transition.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
- UTC offset
- The local clock's difference from UTC on the date and in the location in question.
Wenbu · birth time and time zones ↗Wenbu · calculation conventions ↗
See the claim and source notes
Wenbu rejects ambiguous or nonexistent local input times.
rejects these ambiguous or nonexistent inputs
An explicit UTC offset can be supplied when needed.
supply an explicit UTC offset
The methodology asks readers to check both the inputs and conventions.
先核对输入与计算规则
Sources and review scope
Wenbu drafted and checked this article in Codex. The source list records the scope of the review.
- Current complete zh canonical article ↗Current public original and earlier additions; add substantial coverage without repeating or replacing them. · 2026-11-11 · Fetched text
- Current complete en canonical article ↗Current public original and earlier additions; add substantial coverage without repeating or replacing them. · 2026-11-11 · Fetched text
- Wenbu · birth time and time zones ↗Existing editorial and boundary examples · 2026-11-11 · Fetched text
- Wenbu · calculation conventions ↗First-party implementation; not evidence of predictive accuracy · 2026-11-11 · Fetched text
Check a time in the BaZi calculator
Choose “Other region / custom timezone” and enter -04:00 and -05:00 separately. Keep both candidate instants and the day-boundary setting.
Check a time in the BaZi calculator ↗