Guǐ

The cycle of ten ends with 癸 (Guǐ), yin water. 三命通會 卷二 treats that place as meaningful and says the whole round of yin and yang comes to its end here and begins turning back toward the start. Above it is rain and dew, below it is springs. 淵海子平 teases that picture, asking whether 癸 is really just rain and dew when, with roots in 亥 or 子, it becomes a river.

至弱, weakest of all, is said of the stem's own nature and comes with a turn at once: the commentary says that this thinnest of waters reaches the Ford of Heaven. Its power is a Dragon's power of moving water, so wherever 甲, 乙, 寅 or 卯 stand in the chart the water gets used to feed wood, hold fire, wet earth and nourish metal. Fire and earth therefore hold no terror, and metal gets a shrug, since 癸 neither depends on 庚 and 辛 nor minds many of them. The final clause is technical: a combination of 戊 and 癸 into fire counts as real only if the fire has a root.

Because 庚 and 辛 are the two Resource stems for 癸, the line about them waves away a pair that the same table calls nourishing. 戊 is a Direct Officer here and 壬 a Rob Wealth. A reader checks for wood first, given how much the commentary makes of it, and then asks whether fire has any footing. The calculator puts 長生, the stage of birth, at 卯 and 死, the stage of ending, at 申, where 三命通會 says the metal and earth of that branch wall the water in, and it cites an older line, 水不西流, water does not run west.