What books do fortune tellers use when they tell their fortune?

There are many skills. Take the most common eight-character fortune-telling as an example, which involves many related books, such as The True Solution of Zi Ping, Yuan Hai Zi Ping, Descending the Essence of Heaven, Shenfeng Tongkao, Poor Tongbao Mirror, The Source of Numerology, Five Elements and Three Life Meetings, etc. These are all too common.