Adoption of the Gregorian calendar for secular use occurred in Eastern Orthodox countries as late as the 20th century and some religious groups in some of these countries still use the "old style" (O.S.) Julian calendar for ecclesiastical purposes. The Kingdom of Bulgaria changed from the Julian to the Gregorian calendar during the First World War on 31 March 1916, where the next day was 14 April 1916. The Ottoman Empire's Rumi calendar, used for fiscal purposes, was realigned from a Julian to a Gregorian starting on 16 February/ 1 March 1917. The beginning of the year was reset to 1 January starting in 1918.
Month calendar consists of both a lunar calendar and a solar calendar. The Khmer solar calendar is used more commonly than the lunar calendar. There are 12 months and the numbers of days follow the Julian and Gregorian calendar. The Khmer lunar calendar contains 12 months; however, the eighth month is repeated (as a "leap-month") every two or three years, making 13 months instead of 12. The Tongan calendar is based on the cycles of the moon around the earth in one year. The months are: The Sinhala calendar is the Buddhist calendar in Sri Lanka with Sinhala names. Each full