Swedish calendar Julian calendar. An extra day was added to February in the leap year of 1712, thus giving it a unique 30-day length (February 30). In 1753, one year later than England and its colonies, Sweden introduced the Gregorian calendar. The leap of 11 days was accomplished in one step, with February 17 being followed by March 1. Easter was to be calculated according to the Easter rules of the Julian calendar from 1700 until 1739, but from 1700 to 1711, Easter Sunday was dated in the anomalous Swedish calendar, described above. In 1740, Sweden finally adopted the "improved calendar" already
Calendar reform months and replaced the intercalary month with an intercalary day to be inserted within February every four years. This produced a noticeably more accurate calendar, but it had an average year length of 365 days and 6 hours (365.25 d). This had the effect of adding about three-quarters of an hour every four years. The effect accumulated from inception in 45 BC until by the 16th century the northward equinox was falling on March 10 or 11. Under Pope Gregory XIII, the leap year rule was altered: century years which are not divisible by 400 would be common years. So