Hidden stems(支藏干)

The rules come from a single table that divides each month's energy among its hidden stems. Each branch has residual, middle, and main energy: Ja (子) contains Im (壬) · Gye (癸), Myo (卯) contains Gap (甲) · Eul (乙), and Yu (酉) contains Gyeong (庚) · Sin (辛), while O (午) contains three stems: Byeong (丙) · Gi (己) · Jeong (丁). The other branches also contain two or three stems. The chart above covers all twelve branches, listing the main energy, or primary stem, first and the other stems after it.

Put simply, these are the “characters inside a branch”. Heavenly stems are visible on the surface, while earthly branches are the ground they stand on. Hidden stems describe the stem energies mixed into that ground. In saju, energy present beneath the surface is said to “have roots”, providing strength to draw on when you need to hold steady.

Seowoon's engine uses hidden stems in three ways. First, a branch's Ten God is determined by its primary stem — what In (寅) represents for you depends on the Gap (甲) within it. Second, when assessing rooted support for Day Master strength, the engine looks for the Day Master's element in all recognized hidden stems, not just the primary stem. Third, chart structure gives priority to hidden stems in the month branch that also appear among the visible heavenly stems. Residual stems in Ja · Myo · O · Yu · Hae are excluded from determining chart structure because the engine does not separately calculate which stem governs the birth date.

In Ja (子) · O (午) · Sa (巳) · Hae (亥), the branch and its primary stem have different yin-yang polarities. Ja (子) is a yang branch, but its primary stem, Gye (癸), is yin, so determining its Ten God from the primary stem gives a different result than using the branch's surface polarity. Seowoon uses the primary stem and notes this below the chart.

Seowoon's free “Day Pillar” reading shows each hidden stem in your birth day's branch and its Ten God relationship to your Day Master. It lets you see how the single pattern on the surface differs from the several patterns beneath it.

The claim that “including hidden stems gives a saju sixteen characters” counts hidden stems as equal to the visible characters. In saju, hidden stems are underlying components, so they are counted differently.Seowoon counts only the eight visible characters when tallying the five elements, and uses hidden stems only to identify Ten Gods, roots, and chart structure. A branch with more hidden stems is not necessarily better — branches like Ja · Myo · Yu contain just two stems of the same element, making their inner and outer patterns consistent and often easier to read.