Why the Hour Pillar needs a clock time
A complete Four Pillars chart uses four stem-branch pairs: year, month, day, and hour. The first three can be derived from a calendar date, a place, and the solar-term rules that fix the Month Pillar. The Hour Pillar is different. Traditional two-hour watches (시진) assign a branch to a range of clock time, so the hour stem and branch cannot be confirmed when that time is missing. Leaving the fourth pillar blank is a statement about missing input, not a judgment about the person.
What year, month, and day can still show
Without an hour, a calculator can still print the Year, Month, and Day pillars and count the stems and branches that are present. Those six characters are enough to talk about calendar structure: which solar term the month belongs to, which day stem is the day master in the traditional layout, and how the visible Five Element counts look on the known pillars. They are not enough to complete hidden-stem lists that depend on the hour branch, and they are not a full eight-character chart.
Why guessing an hour is not the same as knowing it
Some readers try to recover a missing hour from later life events. That practice is an interpretive estimate. It starts from a story the reader already believes and then picks a watch that seems to fit. It does not retrieve a hospital record or a civil register. If two programs propose different hours, the difference is a difference of method, not proof that one of them found the historical minute.
How MUN treats a missing hour
The free calculator on this site does not invent an Hour Pillar when the birth time is unknown. Public essays that mention the hour say so only as a structural fact. Traditional readings that lean on children, later life, or a finely split day master often use the hour pillar; those topics should stay marked as incomplete when the time is missing. This is an editorial limit, not a claim that an hour can be deduced from personality.
What to record when you do know the time
If a time is known, write the source next to it: a family notebook, a hospital paper, or a civil document. Also write the place, because local clock time and daylight-saving rules change which watch a minute falls into. Two people born on the same civil date in different time zones can receive different hour branches after conversion. The calendar math is reproducible only when the input and the correction rule are both stated.
Limits of a three-pillar chart
A three-pillar table is still a calendar artifact. Traditional Myeongri may attach character or timing meanings to those pillars, but that vocabulary is cultural convention, not a scientifically validated prediction. Medical, legal, and financial decisions should not rest on a partial chart, and they should not rest on a completed chart either. The honest public sentence is: these are the stems and branches we can calculate from the date we were given.