ACCURACY
True solar time in BaZi
True solar time adjusts a recorded civil clock time for daylight saving, longitude within the time zone and the equation of time.
Historical time zone first
The process must begin with the birthplace's IANA time zone for the actual birth date. Modern offsets cannot safely be applied to historical births.
Longitude correction
The birthplace longitude is compared with the standard meridian of the historical UTC offset. Each degree corresponds to roughly four minutes of solar time.
When it matters
The adjustment changes a pillar only when the corrected time crosses a day or two-hour branch boundary. Different BaZi schools may choose civil or true solar time.