Why saju apps disagree about your chart
Ever entered the same birth date into two saju tools and gotten a different hour pillar? One of three things caused it: solar-term month calculation, longitude correction, or historical clock corrections. The last one — daylight saving and the 1954-1961 meridian era — is where most tools stop. Check your own birth below.
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The three places calculations split
Solar-term month pillar
The month pillar is divided by solar terms, not calendar months. A birth before Ipchun belongs to the previous animal year, and the month turns on the exact minute a term begins. Tools that split by date alone go wrong for anyone born within days of a term boundary.
Longitude correction (~30 min)
Korea keeps time on the 135°E meridian while the country sits near 127.5°E, leaving roughly a 30-minute gap between clock time and true solar time. Without this correction, births near an hour boundary land one pillar off.
Historical clock corrections (usually missing)
Daylight saving ran in 12 periods between 1948 and 1988, and from 1954-03-21 to 1961-08-10 the standard meridian itself was 127°30′E. In both cases the recorded clock time differs from modern standard time, and a tool without those tables keeps getting those births wrong.
Frequently asked
Why do saju apps disagree about my chart?
Three places split the calculation: whether the month pillar follows solar terms, whether the ~30 minute gap between Korea's standard meridian (135°E) and its true longitude (~127.5°E) is corrected, and whether the historical clock changes are applied — the 12 daylight-saving periods between 1948 and 1988 and the 127.5°E standard-meridian era of 1954-1961. The last one is where most tools stop.
Does daylight saving really affect a saju chart?
Yes. During those windows the clock ran an hour ahead of true time, so feeding the clock reading in directly shifts the hour pillar. Measured across a day, roughly half of clock times land on a different hour pillar, and births near midnight shift the day pillar too.
Why is 1954-1961 handled separately?
Korea's standard meridian in that era was 127°30′E (UTC+08:30), adopted on 1954-03-21 and reverted to 135°E on 1961-08-10. Clocks then ran 30 minutes behind today's KST, so a calculation that assumes modern standard time lands in the wrong place.
Which result is correct, then?
The one that applies the historical corrections is closer to the sky at the actual moment of birth. That said, schools differ on hour-pillar boundaries (how late-night 자시 is split), so for a birth near a boundary it is worth holding both readings in view.