A metal stem that opens Dui
The line at 247.5 between Shen and Geng is a trigram border; Dui begins at Geng. Dui is the lake, the west, metal; its mountains are Geng at 255, You at 270 and Xin at 285. Geng is the yang, outward metal of the group, the edge before quiet You.
A stem has no animal or hour; what Geng has is rank. It is one of the three ji with Hai and Mao, and the three ji are about the dragon first. A range entering from Geng is one of the entries the old masters wrote up most warmly, and the Cui Guan Pian puts the dragon first.
Geng as incoming dragon, as peak, as sitting, and the beam that carries
A Geng dragon enters from the west-south-west. At the entry the master wants a neck that narrows and then swells into the site, not a thin spine. A peak on Geng is read as a metal-shaped hill, rounded and compact; on a south-facing site the Dui side is the white tiger's, so it should be steady and not loom.
The star on Geng is Tianheng, Heaven's Beam, an ordinary star named for the crossbeam carrying a roof. The beam fits the dragon: an entry solid enough to carry the site is what the name describes, and the star confirms it. A broken entry gives the beam nothing to rest on. Zuo Geng xiang Jia puts the back west-south-west, the door east-north-east.
What this means on the ground
For the sitting, read inside the door or behind the stone, three times, middle value, away from steel. For the dragon, go behind the site and read the bearing of the incoming ridge; between 247.5 and 262.5 the entry is Geng.
Inside the mountain, 247.5 to about 251 is close to Shen and the Kun group; 259 to 262.5 is close to You and its noble star; 251 to 259 is clean Geng. Walk the last stretch of ridge into the site and feel whether it narrows and swells or just slopes down flat; only the first is worth having.
Common mistakes
The first is true north: with a west declination a phone reports a Geng sitting as Shen or Kun, and the three ji rank is lost. The second is a stone on 247.5, the line between two trigrams. The third is reading Geng off a map rather than walking the ridge; a dragon is judged by its body, not its bearing.
The fourth is taking three ji as a verdict: Geng is listed because a good dragon from there is highly valued, not because any slope on 255 is good. The fifth is mixing Geng with You, a branch at 270 with a noble star, or with Shen in Kun.
Questions people ask
What direction is Geng on a feng shui compass?
West-south-west, 255 degrees magnetic, from 247.5 to 262.5. Geng is a heavenly stem of metal, the first mountain of the Dui trigram with You and Xin after it, and Shen before it. Its opposite is Jia at 75 degrees.
What does it mean that Geng is one of the three ji?
The three ji are Hai, Mao and Geng, the mountains rated highest for an incoming dragon. A range entering from Geng with a firm neck is one of the best entries. The rank describes a good dragon; it does not improve a poor one.
Which star is on Geng mountain?
Tianheng, Heaven's Beam, the crossbeam that carries a roof. It is an ordinary star; the Tianxing school uses it to confirm a Geng entry solid enough to carry the site, after the ridge has been walked.
If the ridge behind your plot comes in from the west-south-west, book a site reading and Master Zhang will walk the entry with you and tell you whether it is a true Geng dragon.