Foundations
Saju is a Four Pillars system built from birth time, place, and calendrical boundaries.
For this product, the public explanation stays simple while the underlying engine stays strict: year, month, day, and hour pillars are chart facts first, interpretation second.
Year pillar uses an Ipchun-based public rule, with winter-solstice audit data stored internally for QA.
Month pillar always follows solar-term entry boundaries, never lunar month starts.
Location normalization matters because timezone, UTC offset at birth, and DST can alter day or hour interpretation at the edges.