Why BaZi and Saju calculators silently disagree on edge-case birth charts

Most Four Pillars astrology calculators — used in Chinese BaZi and Korean saju readings — agree on the majority of birth chart calculations but diverge significantly at calendar boundaries. The year pillar changes not on January 1 or Lunar New Year but at the precise astronomical moment of Ipchun, meaning day-level rounding can assign the wrong pillar to births hours before that instant. Similarly, births near midnight create ambiguity over which day's stem governs the hour pillar, and most tools pick a convention without disclosing it. Geographic longitude further complicates results, since Korea's civil time zone differs from Seoul's true solar time by roughly 32 minutes, enough to shift a birth into a different two-hour hour-pillar bucket. The author argues that transparency about these conventions and the use of absolute time comparisons rather than date-level approximations are essential for consistent, trustworthy calculations.