The corner trigram and its two branches
The four corner mountains are trigrams in their own right; Kun is the south-western one. On either side sit its own branches: Wei at 210, the goat, and Shen at 240, the monkey. Wei, Kun and Shen make the Kun group, and Kun in the middle is its pure earth, no fire left from Ding, no metal yet from Shen.
Kun and Gen face each other across the dial, both earth, both corners. Some manuals treat that line as a thing to avoid; the form school looks at what stands on it instead.
Kun as sitting, as facing, as a peak, and the weight of the axe
Sitting on Kun with the door on Gen is how this mountain is usually met. The back then wants a broad, low, settled rise to the south-west, not a sharp cone. Facing Kun from Gen, whatever hill stands on the south-west is the facing peak.
The star on Kun is Tianyue, Heaven's Axe, an ordinary star named for the axe of authority and judgement. This school uses it to weigh a Kun peak: a square, heavy, flat-topped hill on 225 is what the name describes, and the star confirms it. A thin or jagged hill there gets no rank from the star. A facing towards Tianshi on Gen, a noble star, still needs a real hill to mean anything.
What this means on the ground
Read from inside the door, back to it, or behind the stone along its face: three readings, keep the middle, keep clear of steel. Then find the band: 217.5 to about 221 is close to Wei; 229 to 232.5 is close to Shen and its metal; 221 to 229 is clean Kun.
With a house backed on Kun, walk round to the south-west and see what is behind you: ground that rises gently and stays, or a drop, a gap, a road cut through. For a shop with its door on Kun, stand in the doorway and look at 225 across the street: a solid building is one thing, a gap between towers another.
Common mistakes
The first is mixing Kun with Wei and Shen; all three are the Kun group, but only 217.5 to 232.5 is Kun itself. The second is true north: with ten degrees of declination a true-north phone reads a Kun house as Shen. The third is sitting a stone at 217.5 or 232.5, on a line.
The fourth is refusing a Kun or Gen door on the strength of a book, or accepting one because the book says south-west is for the mother; neither looks at the ground. The fifth is facing Gen for its Tianshi when there is only a car park on 45 degrees.
Questions people ask
What direction is Kun on a feng shui compass?
Due south-west, 225 degrees magnetic, from 217.5 to 232.5. Kun is one of the four corner trigrams, earth by element, with Wei and Shen on either side. Its opposite is Gen at 45 degrees, so a Kun back pairs with a Gen door.
Is a south-west facing house bad feng shui?
No direction is bad in itself. A door on Kun is judged by what it sees: the foreground, the water, the building or hill on 225. The form school reads those first; a book rule is not a reading of your house.
What is Heaven's Axe on Kun mountain?
Tianyue is the star on Kun, named for the great axe, a sign of authority and judgement. It is an ordinary star, and the Tianxing school reads it only to confirm a heavy, square Kun peak or backing the eye has already approved.
If your house sits with its back to the south-west, send Master Zhang the readings and a photo of the ground behind it, and he will tell you in a site reading what the Kun backing is worth.