What Is The Old Style Calendar. Old style (or o.s.) and new style (or n.s.) are terms used for calendar dates in english language historical studies, for two reasons. The american colonies adopted the gregorian calendar in 1752, shifting the start of the year from march 1st to january 1st.
During certain times in history, the julian calendar was called the old style calendar. Old style or os is a designation indicating that a date conforms to the julian calendar, formerly in use in many countries, rather than the gregorian calendar, currently in use in most countries.
