Patek follows ISO 8601, according to which weeks start on Monday. Therefore, Week 1 of a year is considered the one that contains the first *Thursday* of that year...
This is because by containing the first Thursday, Week 1 is the first to also contain a majority (i.e, at least 4 out of 7) of its days inside the new year. Given this, the rest of the weekly calendar is uniquely determined; in particular, every year will...
