The time on the clock and the time of the sun are different
The time pillar (時柱) of the saju is determined by the position of the sun. However, the clock we see uses a single standard time for the entire country, which causes a discrepancy with the actual position of the sun.
Korea's standard time is based on 135° east longitude. Since Seoul's longitude is about 127°, it is approximately 8° west, causing the sun to reach its zenith later — when it is noon by the clock, the sun in Seoul has not yet reached its zenith. This difference is about 32 minutes.
Why we ask for the birthplace
If the longitude is different, the correction amount will also differ. Applying the Seoul-based correction to someone born overseas will result in a significant discrepancy in the time pillar. Therefore, the input screen requires you to select your birthplace, and the calculation is based on the longitude and standard time of that city. Currently, there are 56 places in the list.
In places where the longitude varies greatly even within the same country (such as the USA, Russia, Indonesia, etc.), the cities have been divided. 15° of longitude equals one time pillar slot.
If you do not select, the calculation will be based on Seoul. Since most births are domestic, this reduces the chance of error, but if you were born overseas, please be sure to select.
Standard time has changed several times in the past
There is a reason why the correction cannot be calculated simply as 'longitude difference ÷ 15° × 60 minutes'. The standard time itself has varied over different eras.
| Period | What was different |
|---|---|
| Before 1912 | There was no standard time (local mean time) |
| 1954 – 1961 | The standard time was UTC+8:30 |
| 1948 – 51 · 1955 – 60 · 1987 – 88 | Daylight saving time was implemented |
Inyeon-Link does not use a fixed value for the standard meridian, but calculates the standard time that was actually used at that time based on the IANA time zone information of the birthplace. Daylight saving time and past standard times are automatically reflected.
Births just after midnight also consider the date
Since the correction is -32 minutes, those born between 00:00 and 00:32 by the clock will be 23:00 of the previous day in true solar time. If only the time is reverted and the date is left unchanged, it will write the day pillar as '23:00 of the previous day'.
Inyeon-Link will also revert the date in this case. The day pillar indicates the person themselves in saju, so if this is incorrect, almost all compatibility items will be incorrect.
You do not need to know the time
The birth time is optional. If you do not know it, the calculation will be done without the time pillar, and this fact will be displayed on the results screen. There are no items in compatibility that require the time pillar to be written directly, but it does influence the five elements, so if you know it, it is more accurate to include it.
Zodiac compatibility is always the same value regardless of the time — because it only looks at the year branch.