Four Pillars of Destiny uses the calendar, which divides one year into 24 equally with the position of the sun on the ecliptic. This calendar is called the Chinese Ten Thousand Year Calendar. The Ten Heavenly Stems and the Twelve Earthly Branches are the two numerals, which constitute this solar calendar. The ten stems represent the decimal system and the twelve branches represent the duodecimal system. And all of a year, a month, a day, and an hour are expressed in the combination of these two numerals. First, the Heavenly Stems are Wood+, Wood-, Fire+, Fire-, Soil+, Soil-, Metal+, Metal-, Water+, and Water-. These celestial stems have the origin in the Yin dynasty. And these ten stems originate in the number of ten fingers of both hands, and represented ten days when dividing one month into three equally in an ancient calendar. It was the Warring States period that the Five Elements were introduced into the Heavenly Stems.