Adoption of the Gregorian calendar started to make the change from the Julian calendar and towards the Gregorian calendar in 1700, but it was decided to make the (then 11-day) adjustment gradually by excluding the leap days (29 February) from each of 11 successive leap years, 1700 to 1740. Meanwhile, the Swedish calendar would be out of step with both the Julian calendar and the Gregorian calendar for 40 years; also, the difference would not be constant but would change every four years. This system had potential for confusion when working out the dates of Swedish events in this 40-year period. To add to the
Julian calendar ordinary years in the Roman Republican calendar, from January to December, were: Sacrobosco then thought that Julius Caesar added one day to every month except February, a total of 11 more days to regular months, giving the ordinary Julian year of 365 days. A single leap day could now be added to this extra short February: He then said Augustus changed this, by taking one day from February to add it to Sextilis, and then modifying the alternation of the following months, to: so that the length of "Augustus" (August) would not be shorter than (and therefore inferior to) the