Why doesn't every chart change?
A correction changes the Hour Pillar only when the corrected apparent solar time crosses into a different two-hour Earthly Branch window. A large correction may leave the Hour Pillar exactly where it was.
BaZi Chinese Astrology
Why The Hour Pillar Can Differ Between BaZi Calculators
A plain-language explanation of how civil time, daylight-saving time, longitude, and the Equation of Time can change the Hour Pillar near an Earthly Branch boundary, with worked examples from the BaZi Stars calculation engine.
Civil Time vs. Apparent Solar Time
A civil clock time is defined by legal timezone rules, while apparent solar time tracks where the Sun actually is at the birthplace. Two cities in the same timezone can experience solar noon minutes apart because of their longitude.
Why Daylight-Saving Time, Longitude, and the Equation of Time Matter
Daylight-saving time is part of the historical civil offset and should be applied once. Longitude correction depends on the birthplace, not the timezone. The Equation of Time is a seasonal astronomical drift that can add or subtract up to about 16 minutes.
When Does a Correction Cross a Boundary?
The Hour Branch changes only when the corrected apparent solar time crosses one of the two-hour Earthly Branch boundaries at 01:00, 03:00, 05:00, and so on. A correction can be large and still leave the Hour Pillar unchanged if the birth time sits well inside a branch window.
Frequently Asked Questions
Why do different BaZi calculators disagree?
Calculators can use different assumptions about birth time, daylight-saving time, longitude correction, or solar-time correction. Each can be internally consistent yet produce a different Hour Pillar near a boundary.
Why does this application use apparent solar time?
BaZi Stars uses a deterministic model based on the historical civil time, the birthplace longitude, and the apparent position of the Sun. It is one traditional approach, not the only valid one.
Can two calculators both be internally consistent?
Yes. Two calculators can each follow a coherent method and still disagree on a boundary case. The difference usually comes down to whether and how each one applies longitude correction, daylight-saving time, and the Equation of Time.
Does daylight-saving time get applied twice?
No. Daylight-saving time is part of the historical civil UTC offset for the birth date and is applied once during the conversion to UTC.
Is this the only correct approach?
No. BaZi has been practiced for centuries with a variety of timekeeping methods. This page explains the method BaZi Stars uses so practitioners can compare it with other calculators.