- Use the local clock time recorded at the birthplace.
- Confirm whether that city observed daylight saving on that date.
- Preserve both the recorded time and the derived standard time.
1. What daylight saving changes
Daylight saving advances legal clocks, commonly by one hour but sometimes by another amount. A birth record normally preserves that legal clock reading. The calculation record should show the source time, the applied DST offset and the restored standard time separately.
| Recorded clock | DST rule | Standard time | Possible effect |
|---|---|---|---|
| 03:20 | +60 minutes | 02:20 | May cross from Yin to Chou hour |
| 15:40 | No DST | 15:40 | No DST change |
2. Why city and date both matter
Countries and regions have introduced, suspended and changed DST rules at different times. A current phone setting is not reliable evidence for a birth decades ago. Historical time-zone data must be matched to the city and date.
3. Boundary-review workflow
- Record the original clock time exactly as known.
- Confirm the historical UTC and DST rule for the city.
- Restore standard time, then apply the disclosed longitude and equation-of-time method.
- If any stage crosses a branch boundary, retain both candidate charts.
Do not guess: if the source record does not say whether DST was already reflected, mark the input uncertain and compare candidates.
4. This is not Beijing-time conversion
Restoring a city's legal standard time is different from converting the instant to China Standard Time. BaZi schools may differ on solar correction, but neither step requires erasing the birthplace's original civil record.