Case 11 of 26
True-solar crossings
Chengdu: clock time crosses an Hour Pillar
Historical DST and western longitude move 11:30 back to 09:26.
Boundary question
Can true-solar correction change the branch used for the Hour Pillar?
Yes. The corrected time falls in Si Hour rather than the branch suggested by an uncorrected late-morning clock.
Synthetic input
Recorded facts
- Date
- 1990-06-15
- Recorded time
- 11:30
- Location
- Chengdu, China
- Time zone
- Asia/Shanghai
- Longitude
- 104.0665°
- Gender input
- Male
Pinned expected facts
Verified output
Year
庚午
Month
壬午
Day
辛亥
Hour
癸巳
- Day Master
- 辛
- True solar time
- 1990-06-15 09:26
- Total correction
- -123.76 minutes
- Historical offset
- UTC+09:00 · DST 60 min
- Luck direction
- 顺排
- Reference Jie
- 小暑 · 1990-07-07 17:00:28
- Luck start
- 1997-11-23 05:54:14
Reading the boundary
What this case means for your own chart
This is the first case in the suite where the correction changes an answer rather than just moving a number. A record logged at 11:30 in Chengdu during the 1990 daylight-saving window corrects back to 09:26 true solar time, which is a different two-hour branch from the one the clock reading suggests.
The compounding is what makes it work. Chengdu sits well west of the 120°E meridian that China's clocks were set to, so longitude pulls the time back. The daylight-saving hour pulls it back again. Together they move the record by about two hours, which is a full hour-pillar width.
For readers, this is the case that answers the question of whether the correction is cosmetic. It is not. A chart built from the raw 11:30 reading and a chart built from the corrected 09:26 differ in the hour pillar, and the hour pillar is where the tradition places a great deal of time-sensitive material.
What does not change here is instructive too. The year, month, and day pillars are unaffected, because the correction stayed inside the same day. That is the common shape of an hour-pillar crossing: a single column moves while the rest of the chart holds steady, which makes it easy to overlook when comparing two charts that agree on three pillars out of four.
Check your own record
- If you were born in western China during a daylight-saving year, expect a correction large enough to move your hour pillar.
- Check whether your chart's hour pillar is derived from your clock reading or from a corrected time. Ask the tool, or read its method page.
- If the two disagree, the corrected time is the one this engine uses, and it states that openly rather than hiding the correction.
Which convention is in play
- Calculation fact
- The pinned engine returns 09:26 true solar time for this 11:30 Chengdu input, placing the record in Si Hour rather than the branch the raw clock reading implies.
- Convention
- That a two-hour branch governs the hour pillar is mainstream. Whether to apply the solar-time correction before assigning it is where practice divides, and this engine states its position.
- Our explanation
- Calling this the case that proves the correction is not cosmetic is our framing. It follows from the arithmetic rather than from a traditional authority.
Conventions and limits
What this case does — and does not — prove
It verifies
Deterministic reproduction of this input under the named engine version and conventions. A pinned-field mismatch stops the production build.
It does not claim
Universal agreement across Bazi schools, interpretation of a real person, or certainty where the historical record is incomplete.
tyme4ts 1.5.2 · cantian-tymext 0.0.27 · sect 2 day boundary · BaziCalculator.ai NOAA/IANA true-solar adapter
calculation-benchmarks-v1 · reviewed 2026-09-05