What goes into the correction?
The recorded local date and clock time are resolved to an instant using the selected IANA time zone. Apparent solar time then uses longitude and the Sun’s hour angle. The result includes the equation of time and the total difference from the recorded clock.
How do I enter longitude?
Use decimal degrees, east positive and west negative. For example, 120.15 is east of Greenwich, while New York is approximately −74. Longitude is necessary; a city’s time-zone offset is not a substitute.
What happens during daylight-saving changes?
A clock time skipped during a spring transition is rejected. A repeated autumn time needs your choice of first or second occurrence. Historical zone data comes from the browser’s IANA implementation. The displayed solar date is a local solar-clock label, not a new UTC instant.