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However, the Gregorian calendar begins with the year 1. (There is no year “zero”, and the year before AD 1 is 1 BC with nothing in between.) Therefore, its first decade is from AD 1 to AD 10, the second decade from AD 11 to AD 20, and so on. So, although “the 1960s” comprises the years 1960 to 1969, “the 197th decade” spans 1961 to 1970.