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.
Lithuanian calendar month names on this artifact are expressed in symbols, based on natural phenomena and agricultural cycles. (i.e. the sidereal month was divided into three parts). The Julian calendar was used in the Grand Duchy of Lithuania; the Gregorian calendar was adopted by the Polish-Lithuanian Commonwealth in 1586, a few years after its promulgation in 1582 by Pope Gregory XIII. In 1800, following Lithuania's annexation by the Russian Empire, the Julian calendar again became the norm, although a part of ethnic Lithuania left of Nemunas River (Suvalkija) retained the Gregorian calendar (see Aleksotas). The Russian Revolution of 1917 re-instated the Gregorian