As described the Calendar FAQ, February had 30 days in Sweden in 1712.
The picture below shows two pages from a Swedish almanac from 1712.
In the top left corner you see the word "Februarius", and at the bottom of the right page, the 30th day of that month is mentioned.
The two words to the right of the number "30" are:
- "Tillökad", that is, "added".
- "Snöö", that is, "snow". It was customary to include weather forecasts for the entire year in almanacs. Very convenient!
The following is a copy from the church registry in St. Petri Parish in the Swedish town of Ystad:
The text reads: Anno 1712. d: 30 Februarij wijdes fullmächtigen på Jordbärga Svven Hall wid hust Elena Jäppdotter Duue. (That is: "Anno 1712. On 30 February the clerk Svven Hall of Jordbärga was married to Elena Jäppdotter Duue.")
(Taken from www.ddss.nu.)