Historical timezone
The region and date determine historical offset; repeated times require a choice.
XINAN LIFE BOOK · Apparent solar clock
Before reading a chart, understand its starting clock.
Compare the recorded civil clock with apparent solar time. Historical timezone, longitude and equation of time are separate steps. Display precision does not establish record accuracy. Query independently or explicitly reuse your saved details.
Solar-clock correction
Show longitude correction and equation of time separately without double adjustment.
Day-boundary comparison
Preserve full dates and explicitly label shifts to an earlier or later day.
This tool’s method
Astronomy Engine 2.1.19 solar hour angle. IANA historical offset includes DST and is subtracted once. Longitude is unwrapped to the meridian nearest that offset for the date line. Equation of time = apparent minus mean solar time. A settlement coordinate is not a home location or proof of birth-record accuracy.