Sweden did an... interesting version of calendar change. Like Britain, we stuck with the Julian calendar for quite some time. Then we decided to catch up with t

Sweden did an... interesting version of calendar change. Like Britain, we stuck with the Julian calendar for quite some time. Then we decided to catch up with the Gregorian calendar by omitting leap days, starting from 1700 (this would have taken 40 years!). To make matters worse, the scheme was forgotten and 1704 and 1708 were leap years. In 1712, Charles XII decided to sync back to the Julian calendar by having an extra leap day, making a 30-day February, which I think is unique. We then finally went Gregorian by omitting 12 days at the end of February 1753.