Same Birthday, Different Saju Chart?

Start with the date format, recorded local birth time and birthplace. Then compare the time-zone record, the type of solar-time correction and the rule for changing the day. A difference in one of these settings can produce a different pillar even when both sites received the same birthday.

Enter the time as it was recorded. Do not subtract a city correction yourself before entering it: a calculator that also applies that correction would subtract it twice. Our English calculator accepts a Gregorian date; check the date conversion first if your record uses the lunar calendar.

Longitude correction adjusts standard clock time toward local mean solar time at four minutes per degree from the time zone's standard meridian. True, or apparent, solar time also uses the equation of time, a date-dependent difference between mean and apparent solar time.

These are separate operations. The default calculator here applies longitude correction when the location's longitude is available, but not the equation of time. The result's correction details show what was used. This describes our calculation convention; it is not a claim that every Saju school must use it.

Use June 15, 1990, Seoul, with longitude 126.978°E. The historical standard offset is UTC+9 and daylight saving is not in effect. The longitude adjustment is about minus 32 minutes 5 seconds; the equation of time is not applied in this example.

A recorded 15:15 becomes 14:42:55, moving from the clock's 申 (Monkey) interval into 未 (Goat). A recorded 23:30 becomes 22:57:55, still in 亥 (Pig). A recorded 00:15 becomes 23:42:55 on the previous date. Under our midnight-after-correction convention, that last example uses the previous day's Day Pillar.

The same number of minutes does not apply to every city or birth year. Use your own birthplace and inspect the correction details instead of copying Seoul's adjustment.

Time-zone and daylight-saving rules change. We use the IANA time-zone record for the chosen location and birth date rather than assuming today's UTC offset applied in the past. Historical records have limits, particularly for older dates, so the calculation trace is more useful than a blanket promise of perfect accuracy.

Some Saju conventions change the Day Pillar at 23:00; others use midnight. Our default uses midnight after the time correction. A time in the 23:00 hour is therefore not automatically assigned to the next day.

The two-hour 子 (Rat) interval crosses midnight, but naming that interval does not by itself tell you which day-boundary rule a calculator uses. Compare the rule as well as the clock correction before treating a different chart as an error.

Choose the unknown-time option when you cannot establish the hour. The Hour Pillar is omitted, and the result marks the limits of what can be calculated. Near a corrected midnight or solar-term boundary, the Day Master, Month Pillar or Year Pillar can also be uncertain.

An approximate time is still an estimate. If you have a documented range, compare its endpoints; if the pillars change within that range, do not treat one selected minute as a confirmed birth time. The chart's calculation and the interpretation of it are separate questions.