The idea behind the module is to simply assist someone with keeping an I Ching journal, not to automatically calculate the hexagrams themselves. For example - you give the I Ching Journal module what the lines are and it's job is to look up the hexagram number(s) for you, nicely highlight any changing lines, and provide an archiveable/searchable record. You can even categorize your entries (well, at least if you enable taxonomy ;-).
Demo site for the I Ching Journal module. If you don't know what the I Ching is and would like to learn more, the Wilhelm/Baynes book is a recommendable starting place.