The present timepiece is offered in absolutely stunning condition. A further layer of appeal is granted by the prestigious Orologeria Pisa signature on the Certificate, one of the most prominent Italian watch retailers. Patek Philippe themselves celebrated their collaboration with this revered house in 2007, with a special edition of the Calatrava reference 5296.

The third iteration of the celebrated perpetual chronograph line of timepieces by Patek Philippe, reference 3970 is the heir to legendary 2499, with which it shares the unmistakable case construction characterized by the sculpted lugs. It is however one millimeter smaller than its predecessor: its 36 mm. diameter places it in between reference 1518 (35 mm.) and indeed reference 2499 (37 mm.).

With reference 3970, the dial acquires to new indications: the 24 hours indication and the leap year indication. It is remarkable how these additions do not encumber the dial design: they are ingeniously placed inside the subsidiary dials at 6 and 9, thus keeping the overall look and feel of the dial very similar to that of reference 2499. If anything, they render the two subsidiary counters more balanced thanks to the small designations at 3, 6, 9 and 12.

The Ref. 3970 was produced in four series, the present example is from the fourth and final series.

Beyond being aesthetically pleasing, the new indicators are extremely practical: the 24 hours indication allows the wearer to avoid setting the calendar when the time is around midnight and the calendar gear train is working, which would damage the movement. The leap year indicator is invaluable when setting the perpetual calendar: with earlier models one had to manually proceed to February 28, and then pay attention if the next day would be February 29, in which case he or she would obviously know it is a leap year, or March 1st, in which case it could be any of the non-leap years. Another practical addition is the push-piece for setting the month, while previously one could only proceed one day at a time.