The Equation of Time
True Local Solar Time
Chinese astrology uses the solar time. After the conversion from time zone and the city longitude, the time is not the true solar time, because the solar day is NOT 24 hours even per day in the entire year. We need the equation of time to adjust our birth time to the True Solar Time, which is the Sundial time.
When creating the Personal Birth Data, there is an Sundial button to instantly adjust birth time to the True Solar Time for you.