A stem between two branches
Gui is the narrow water mountain between Zi and Chou. As a sitting in its own right it suits a back ridge that comes down a little east of north, with the stone set on 13 to 17 degrees and the face on Ding, 195 degrees. It is also where a master moves to when a Zi reading sits too close to 7.5 degrees. A stone cannot stay on the line between two mountains, so it is turned a degree or two onto Gui, provided the ridge and the water allow it. Walk up behind the stone: the slope should come down to it in one piece, not broken by terraces or a cut bank.
Tiandao and the order of the dragon
Tiandao means Heaven's Way: order, rule, things moving as they should. It is a common star, and in the Tianxing reading a common star does not raise a site; it is held up against the form to see whether the two agree. A dragon that enters from Gui should come in by steps, each knot lower than the last, each turn clean, until it opens into a level platform. Water that arrives from Gui should come in a measured curve across the front, not in a straight rush. When the dragon is tangled, the water straight and the platform tilted, the ground has no order, and the star called Heaven's Way does not supply any.
What this means on the ground
At a grave, stand behind the stone and sight along its face; at a house, stand inside the front door with the door at your back. Keep the luopan level, keep steel away from it, and take three readings. Facing 195 means sitting on Gui. Then see where inside Gui you have landed. From 12 to 18 you are in the middle of the mountain. From 7.5 to 10 you lean on Zi, under Tianlei. From 20 to 22.5 you lean on Chou, and here the change is larger: Chou is earth, Gen and Tianchu, and the 22.5 line is a border between two trigrams. We keep well inside that line.
Common mistakes
The common error is to call anything roughly north Zi. Gui is 15 degrees from the centre of Zi, and a house door at 200 degrees is facing Ding and sitting on Gui, not on Zi. Phone compasses set to true north make this worse: with a declination of 12 degrees the whole site shifts by most of a mountain. Another error is to look up Gui in a table of lucky stems from a Bazi chart. A day stem of Gui in a birth chart has nothing to do with the mountain Gui on the luopan. A third is to read the facing from the street; it is taken inside the door or behind the stone.
Questions people ask
What direction is Gui on a feng shui compass?
Gui is 15 degrees magnetic, north by north-east, covering 7.5 to 22.5 degrees. It sits between Zi and Chou and belongs to the Kan trigram. A stone on Gui faces Ding.
Is Gui the same as north in feng shui?
No. Gui is a separate mountain, 15 degrees east of due north. It shares the Kan trigram and the water element with Zi, but it has its own star, Tiandao, and its own facing, Ding.
What is the star on Gui mountain?
Tiandao, Heaven's Way, a common star. Our school uses it to test whether the dragon and water on Gui come in with order; it does not add anything to a site on its own.
Not sure whether your door sits on Zi or Gui? Send three readings and a photo from inside the door, and Master Zhang will settle it in a site reading.