The yarrow oracle method as related through Ta Chuan (the Great Treatise) is attributed to Kung-fu Tze. The querent begins with 50 (fifty) yarrow stalks and manipulates them in a prescribed and probabilistic manner until few remain. This remainder may take on one of exactly four possible symbolic values, though the actual number of stalks may vary according the the precise form of the ritual. The symbolic values are sometimes referred to as 'xiang.' Each manipulation of the stalks produces one line of a six-line figure commonly known as an hexagram. Thus, six "randomly-generated" xiang produce an hexagram. Once generated, the querent references the scripture according to that hexagram.
In recent years, capable persons have employed mathematics to reduce the yarrow-stalk oracle to the raw probabilities it produces for each of the four types of lines that may obtain from a divination operation. The following table is a description of those lines and their relative probability of occurrence in divination:
dynamic yin, represented by '6' and symbol ⚏ ( 4 in 64 = 0.0625)dynamic yang, represented by '9' and symbol ⚌ (12 in 64 = 0.1875)static yang, represented by '7' and symbol ⚎ (20 in 64 = 0.3125)static yin, represented by '8' and symbol ⚍ (28 in 64 = 0.4375)
The graphic depicted here shows the xiantian arrangement overlaid on a tableau of concentric squares, each discretely colored. This presentation is remarkable in that it implicitly encodes the yarrow oracle probabilities; i.e. each ring comprises a specific proportion of the hexagrams as shown in the table above.