<Tr> <Td_colspan="2"> This box: <Ul> <Li> view </Li> <Li> talk </Li> <Li> edit </Li> </Ul> </Td> </Tr> <Ul> <Li> view </Li> <Li> talk </Li> <Li> edit </Li> </Ul> <P> The Gregorian calendar is internationally the most widely used civil calendar . It is named after Pope Gregory XIII, who introduced it in October 1582 . </P> <P> It was a refinement to the Julian calendar involving an approximately 0.002% correction in the length of the calendar year . The motivation for the reform was to stop the drift of the calendar with respect to the equinoxes and solstices--particularly the northern vernal equinox, which helps set the date for Easter . Transition to the Gregorian calendar would restore the holiday to the time of the year in which it was celebrated when introduced by the early Church . The reform was adopted initially by the Catholic countries of Europe . Protestants and Eastern Orthodox countries continued to use the traditional Julian calendar and adopted the Gregorian reform, one by one, after a time, at least for civil purposes and for the sake of convenience in international trade . The last European country to adopt the reform was Greece, in 1923 . Many (but not all) countries that have traditionally used the Julian calendar, or the Islamic or other religious, calendars have come to adopt the Gregorian calendar for civil purposes . </P>

Who was the only person allowed to adjust the calendar