Yarrow Stalk Method

Yarrow casting derives a line value through successive division and remainder operations. Three changes are three rounds producing one line, not three separate lines; six completed line values form a hexagram. Distinguishing those levels explains eighteen changes and prevents confusing an intermediate remainder with final polarity.

Xi Ci describes fifty stalks with forty-nine in use. In the common procedure, set one aside, split the rest, hang one, count in fours and remove remainders. Repeat with the remaining stalks for three changes, then divide by four to get 6, 7, 8 or 9. Repeat for six lines bottom to top: eighteen changes.

Under the common equally likely remainder model, 6/7/8/9 have probabilities 1/16, 5/16, 7/16 and 3/16. Three fair coins give 1/8, 3/8, 3/8 and 1/8. Both move on 6 and 9 but differ in Old Yin/Old Yang proportions. Yarrow is a casting method; Najia assigns branches and relationships to the resulting hexagram.

Arithmetic example: from 49, the first change removes 5 or 9, leaving 44 or 40; each later change removes 4 or 8. Removing 9,8,8 leaves 24, divided by four to give Old Yin 6. Removing 5,4,4 leaves 36, giving Old Yang 9. Other combinations produce 7 or 8.

In the common remainder model, the first removal is 9 with probability 1/4 and 5 with 3/4; each later 4/8 removal has probability 1/2. Thus 9,8,8 has probability 1/16 and 5,4,4 has 3/16. The difference from fair coins follows from the stated arithmetic model, not a claim of superior predictive accuracy.