Gregorian calendar It also specifies its epact relative to 1 January, in contrast with the Julian calendar, which specified it relative to 22 March. The old date was derived from the Greek system: the earlier "Supputatio Romana" specified it relative to 1 January. During the period between 1582, when the first countries adopted the Gregorian calendar, and 1923, when the last European country adopted it, it was often necessary to indicate the date of some event in both the Julian calendar and in the Gregorian calendar, for example, "10/21 February 1750/51", where the dual year accounts for some countries already beginning their
Adoption of the Gregorian calendar is only occasionally used today. North Korea from 1997 officially counts years based on the Juche era, the first year of which is 1912. The Republic of China (ROC) formally adopted the Gregorian calendar at its founding on , but China soon descended into a period of warlordism with different warlords using different calendars. With the unification of China under the Kuomintang in October 1928, the Nationalist government decreed that effective the Gregorian calendar would be used. China retained the Chinese traditions of numbering the months and a modified Era System, backdating the first year of the ROC to 1912;