Someone who uses yarrow stalks
to divine an I Ching hexagram
. Sometimes also called a "yarrowmancer".
To produce the hexagram, the oracle divides divide a heap of forty-nine yarrow stalks in two (formally, one would start with fifty and remove one), then cast off one stalk from the right pile (leaving forty-eight total). Next, stalks are removed from each pile four at a time until between one and four stalks remain in each pile. The number of stalks remaining in each of the two piles is then added together with the one removed stalk, producing a sum of either five or nine. If five, a score of three is assigned; if nine, a score of two.
The process is repeated with the cast-off stalks, producing a second score of 2 or 3, and then again with those cast-off stalks, producing a third score. These three scores are then added, producing a number between six and nine. This number determines which kind of I Ching line is drawn. The process then repeats again until six lines are drawn. (Tedious, ain't it?)
In practice, it can be shown that the odds of getting a score of two in any division is 1/4, not 1/2, and the odds of getting a score of three is 3/4. Consequently, the odds of producing a particular I Ching hexagram with traditional yarrow stalks is different than if one uses the more modern method of flipping coins.