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February contains 28 or 29 days. However, three times in history in selected countries, it actually had 30 days.
Sweden (at that time Finland was part of the Swedish realm) planned to change from the Julian calendar to the Gregorian calendar, beginning in 1700 by omitting the leap days for the next 40 years. Thus 1700 was not a leap year in Sweden, however both 1704 and 1708 were leap years contrary to the plan. This brought the Swedish calendar one day ahead of the Julian calendar but still ten days behind the Gregorian calendar. This confusion was reduced when, in 1712, two leap days were added, thus giving this year a February 30. That date corresponded to February 29 in Julian and March 11 in Gregorian counting. The Swedish change to the Gregorian calendar was finally done in 1753.
In 1929 the Soviet Union introduced a revolutionary calendar in which every month had 30 days and the remaining 5 or 6 days were monthless holidays. In 1930 and 1931, it thus had a February 30, but in 1932 the months regained their old lengths.