Celestial time
Why Born Hour calibrates the clock before reading the pillars.
Wall-clock time is not local solar time. Born Hour converts civil time to UTC with IANA zones, including historical daylight saving.
Longitude yields local mean time; the Equation of Time then produces celestial time. Stems, branches, and hour branches are cut on that calibrated instant.
A one-hour shift changes the Hour Pillar and hour-dependent markers. Birth time is required; the system never invents a placeholder hour.