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The cycle of years consists of sixty possible combinations of pairs of characters, a system used since remote antiquity. A second system used reign periods similar to that used in England until fairly recent times. In the sixty-year cycle, the Chinese have used individual characters, the ten stems [tiangan] and the twelve branches (dizhi), paired to provide sixty combinations; thus, the first of the stems, Jia, and the first of the branches, Zi, together form a combination for the first year of the sixty, Jia Zi, and each successive year has another pair designating it for the whole sexagenary cycle when the combination begins again.24 The 'branches' were originally used to designate successive days; however, since the Han, they have been used in combinations for successive years.
Also within that sixty-year repetitive cycle, each individual year, with the five sequences of twelve years, was known, not only by the combination of stem and branch but also, for simplicity, by the animal of the year. Thus, the year 2000 is the Gengchen year as well as being the year of the Dragon. 1988 was and 2012 will also be the year of the Dragon, but neither will be Gengchen years, as this only comes round once every sixty years. For example, the year 2000 was Gengchen, as was sixty years earlier in 1940 and will be again in 2060.
The Chinese years are also referred to cyclically by one of the twelve named animals. Thus, we have the years of the Rat, Ox, Tiger, Hare, etc., the change taking effect from the Lunar New Year, which can fall any time between late January and the middle of February on the Gregorian calendar.
Although the months were divided into two fifteen-day periods, markers for rituals, these periods had no particular relevance to the lives of the common man. What did have marked relevance for the majority of the population was the artificial division of the month into three ten-day periods, used mainly to mark rest days. However, as the seven-day week of the Judeo-Christians does not follow the natural laws by which events and phenomena operate, so it was an alien concept to the majority of Chinese until 1911, when the western Gregorian calendar was introduced by the Republic.
Chinese used sun dials and water clocks from an early date, the latter dependent upon a constant and steady flow through control