The Depths of the Six Channels Really Have Numbers: Six Fen, Five Fen, Four Fen…

The idea that the Six Channels differ in depth is common in classical medicine. What is distinctive in the Mirror Classic of Bian Que is that it gives explicit numbers.

The text says:

Foot Yangming is six fen deep; retain for ten breaths. Foot Taiyang is five fen deep; retain for seven breaths. Foot Shaoyang is four fen deep; retain for five breaths. Foot Taiyin is three fen deep; retain for four breaths. Foot Shaoyin is two fen deep; retain for three breaths. Foot Jueyin is one fen deep; retain for two breaths.

It adds:

The routes by which the hand yin and yang receive qi are near, so their qi arrives rapidly. Their depth does not exceed three fen and retention does not exceed five breaths. All are standardized by bone measure.

Depth and time are bound together

The text does not merely say “six fen deep.” Each depth is paired with a specified number of breaths of retention.

To observe the qi of a given channel, one must therefore not only reach a particular depth but also maintain observation for a defined respiratory duration.

This is completely consistent with the method introduced in the first series: spatial scale and temporal scale must be defined together.

The six Foot Channels form an ordered gradient

From Foot Yangming at six fen down through Foot Jueyin at one fen, the text gives six ordered depth levels. Observation time also generally decreases with depth.

The sequence shows that the author does not rely only on vague adjectives such as “deeper” and “shallower,” but aims to construct an operational stratification.

“Fen” cannot be converted directly into millimeters

The source explicitly says that these measures are “all standardized by bone measure.” Fen here therefore belongs to a proportional bodily scale rather than a fixed metric unit.

Any future validation using modern pulse-diagnostic instruments would first need to calibrate same-body proportion, pressure depth, and sensor contact area. An ancient “one fen” cannot simply be assigned a fixed number of millimeters.

This is one of the clearest expressions of the Mirror Classic’s quantitative ambition

The passage moves “Six-Channel depth” from a symbolic level into a measurement level by specifying depth, respiratory time, and bone measure together.

The next article examines another highly mathematical quantity: how the divisions of the Twelve Lü are calculated from tonal division and She division.