Patek Philippe Annual Calendar / Moon Phase in 18k Yellow Gold Ref. 5146J with Original BoxPatek Philippe introduced its first Annual Calendar, reference 5035, in 1996. This model features functions for the day, date, and month, allowing it to differentiate between months with 30 and 31 days. As a result, it requires manual adjustment only once a year, at the end of February. The innovative reference 5035 was followed by the reference 5146 Annual Calendar in 2005. The key enhancements between the two models include an increase in size from