Swedish calendar

In November 1699, the Government of Sweden decided that, rather than adopt the Gregorian calendar outright, it would gradually approach it over a 40-year period.

Every fourth year, the gap between the Swedish calendar and the Gregorian would reduce by one day, until they finally lined up in 1740.

In accordance with the plan, 29 February was omitted in 1700, but the Great Northern War stopped any further omissions from being made in the following years.

Its improvement was to calculate the full moon and vernal equinox of Easter according to astronomical tables, specifically Kepler's Rudolphine Tables at the meridian of Tycho Brahe's Uraniborg observatory (destroyed long before) on the former Danish island of Hven near the southern tip of Sweden.

[3][4] In addition to the usual medieval rule that Easter was the first Sunday after the first full moon after the vernal equinox, the astronomical Easter Sunday was to be delayed by one week if this calculation would have placed it on the same day as the first day of Jewish Passover week, Nisan 15.