The ten calendar signs and the twelve signs of the zodiac
Jikkan-Jūnishi are a method of placing order on time and space and were created in ancient China. The ten signs called jikkan and the twelve signs called jūnishi, independently or in combination, express dates, years, months, times and directions. The combination of jikkan and jūnishi is also called the sexagenary cycle (eto), but now the term eto chiefly refers only to jūnishi, the signs of which correspond to twelve kinds of animals; rat, ox, tiger, rabbit, dragon, serpent, horse, sheep, monkey, rooster, dog, boar. Saying, “I was born in the year of the dog.” Expresses one’s age, and the animal expressing that year is drown on New Year’s cards. Moreover, when one turns 60, there is the custom of celebrating it as kanreki (which in Japan is actually the 61st birthday, counted at the beginning of the year rather than at the end as in Western countries, hence, kanreki means that one has lived 60 complete years), because the combination of jikkan, on the decimal scale, and jūnishi, on the duodecimal scale, complete a full cycle and return to the original combination of the year when one was born.
──『日本文化を英語で紹介する事典 A Bilingual Handbook on Japanese Culture【第３版】』杉浦洋一＋John K. Gillespie（ナツメ社／2004年）
