Chinese legend holds that at any one time, there are only five people in the world who have mastered the art of Tie Ban Shen Shu.
Chinese legend also holds that learning Tie Ban is problematic, as the literary sources are deliberately obscured to prevent novices from easily gaining this precious knowledge.
The procedures for arriving at the correct texts are based on the Four Pillars (Ba Zi), which include the ten Heavenly Stems and twelve Earth Branches, numerology, the 64 hexagrams of the I Ching and the Six Familial Relationships of Chinese metaphysics.
Tie Ban's emphasis on the specific quarter-hour (fifteen-minute segment) of birth ensures the relatively high degree of accuracy, in comparison with other divination methods.
[1] When the time of birth was not recorded, it could be calculated based on information from the parents, siblings and life experience, down to the quarter-hour period.