How the oracle is cast
Fifty stalks, six lines, and a count that takes as long as it takes.
The oldest way of consulting the Book of Changes uses fifty dried yarrow stalks. One is set aside at the start and takes no further part — the observer — leaving forty-nine in play. Those forty-nine are divided, counted, and gathered again and again until six lines have been built, and the six lines are the answer.
Building one line
The forty-nine stalks are divided roughly in two — one heap for heaven, one for earth. A stalk is taken from the earth heap and held apart for the human place between them. Then each heap is counted away four at a time, and the remainders are set aside. This whole operation happens three times for a single line. The stalks that remain at the end resolve to one of four numbers: six, seven, eight or nine.
Seven and nine are yang — solid lines. Six and eight are yin — broken lines. The distinction that matters most is old against young: nine and six are old lines, lines at their extreme, and an extreme is where change begins. These are the moving lines. A nine is a solid line about to break; a six is a broken line about to close.
Building the hexagram
The count repeats six times, and the figure grows from the ground up — the first line cast is the bottom line. Six counts of three passes each is eighteen separate divisions of the stalks, and with practice the whole cast takes something like twenty minutes. The slowness is not an inefficiency to be engineered away. Eighteen repetitions of the same quiet operation settle the mind on the question the way pacing settles a decision, and by the time the sixth line lands, the question has usually ripened into its real form.
If any lines came up moving — sixes or nines — they are read as the live points of the situation, and flipping each one to its opposite produces a second hexagram: where the situation is headed. A cast with no moving lines is a situation at rest.
What this site does
The cast page performs the yarrow count faithfully — the same divisions, the same probabilities, the same six-line build — with the waiting kept in. The traditional yarrow probabilities are not symmetric: a moving yang (nine) is three times as likely as a moving yin (six), a bias toward the light that coin methods flatten out. This site keeps the stalks' arithmetic.
When the figure is complete, reading a cast explains what to do with it, and every hexagram's full chapter is in the reference.