Patek Philippe Perpetual Calendar, Ref 3941 in Yellow Gold, Circa 1990

In 1985 Patek Philippe introduced its new perpetual calendars, references 3940 and 3941, whose designs were a complete break from the brand’s iconic perpetual calendars first launched in 1941 with reference 1526. These new models featured an elegant slim stepped case. The days and months were no longer indicated through an aperture on the top part of the dial but via two subsidiary dials at 9 and 3 o’clock respectively.Reference 3940 features a solid case back whereas reference 3941 is fitted with a glazed display back. These glazed display backs are not numbered and Patek Philippe applied the case numbers inside the case underneath the bezel. In response to an increasing demand for both case backs, Patek Philippe later produced the model with both case back options. Production of reference 3941 ceased in 1990 as there was no longer a difference between the two models, and consequently very few examples bearing reference 3941 exist. In fact research shows that only 35 models of this reference are known to date.