The classical procedure uses fifty dried yarrow stalks. One is set aside; the rest are divided, counted out in fours and set between the fingers through three operations that produce one line, and the whole is repeated six times. The arithmetic is designed so that the four possible outcomes are not equally likely. The simpler three-coin method, which spread from the Song dynasty onwards, tosses three coins six times and is much faster, but it flattens those probabilities, so the two methods do not give identical odds of a changing line. Practitioners argue about whether this matters.
Interpretation was never left to the diviner alone. Commentaries multiplied: Wang Bi in the third century, who read the hexagrams as situations rather than omens; the Song Neo-Confucians, for whom Zhu Xi insisted the book be understood first as a divination manual and only then as philosophy; and the numerological tradition of Shao Yong, whose arrangement of the sixty-four figures caught Leibniz's attention in 1703 as a representation of binary arithmetic.
The route into modern Western reading runs through one edition. Richard Wilhelm, a German missionary in Qingdao, translated the book into German in 1924 with the help of the scholar Lao Naixuan, presenting it through the Neo-Confucian commentarial tradition he had been taught. Cary Baynes rendered Wilhelm's German into English, published in 1950 in the Bollingen Series, with a foreword by Carl Jung that used the book to introduce his notion of synchronicity, meaningful coincidence not explained by cause and effect. That foreword, more than the translation, made the book a fixture of Western counterculture from the 1950s onwards, and it means many English readers meet a Chinese classic at two removes and framed by a Swiss psychiatrist.