Chen sits directly opposite mountain 22, Xu, twelve positions and a hundred and eighty degrees around the ring: in compass school feng shui a building or a grave is described by this sitting-and-facing pair, the back set toward Chen and the front opened toward Xu, and Stephen Skinner's account of the luopan treats the correct reading of a sitting-facing pair as the compass's most basic function, prior to any of the finer rings layered around it. The twenty-four mountain ring itself interleaves three different kinds of position at fifteen degrees each, twelve Earthly Branches, eight Heavenly Stems and four corner trigrams, and Chen belongs to the branch layer, the oldest and most complete of the three, present at every one of the twelve thirty-degree sectors the ring divides the circle into.
As a storehouse branch, Chen is read in Flying Star and Four Pillars applications not only for the direction it names but for the hidden stems it carries within it, since a branch's concealed qi can be drawn on by a chart or a siting even when the branch's visible element alone would not obviously support the reading, which is why storehouse and growth branches are treated as carrying more than their single surface element suggests. Compass school practice treats the fifteen-degree seam between one mountain and its neighbour as a genuine hazard rather than a rounding error: a sitting or facing line falling exactly on that boundary, called an empty or straddling line, is read as drawing on the qi of both adjacent mountains at once rather than cleanly on one, and Stephen Skinner's account of the luopan treats avoiding a seam-line reading as one of the instrument's basic disciplines, checked before any of the finer rings above the twenty-four mountains are consulted at all.