In light of Q's posts from Oct 4 and the ensuing shill/concernfag/chicken little sky is falling week:

>Catholic states such as France, the Italian principalities, Poland, Spain (along with her European and overseas possessions), Portugal and the Catholic states of the Holy Roman Empire were first to change to the Gregorian calendar. Thursday, 4 October 1582 was followed by Friday, 15 October 1582, with ten days skipped.

https://en.wikipedia.org/wiki/Adoption_of_the_Gregorian_calendar