Perpetual calendar chronograph timepieces have always been closely tied to one manufacture, Patek Philippe. Being the first to introduce the perpetual calendar chronograph wristwatch in the 1940s, the firm garnered much attention when they launched the ref. 1518 and 2499. In 1986, the firm released the ref. 3970 replacing the legendary and coveted ref. 2499. With a production of the reference spanning until 2004, the ref. 3970 was introduced in a total of four series over the years.

First series (1986 – 1988) – Features snap on caseback, solid for (3970) and glazed for (3971), in production for a very short time. Dial: Satinated silver, rectangular indexes, “feuille” hands.

Second series (1989 – 1990) – Features screw back case, usually referenced as 3970E or 3971E (“E” for Etanche meaning waterproof). Dial: Satinated silver, rectangular indexes, “feuille” hands, later examples with “Baton” hands.

Third series (1989 – 1995) – Features screw back case with additional sapphire caseback, (ref. 3971 discontinued), after 1990 (lapilated indexes, matching “baton” hands).

Fourth series (1994 – 2004) – Features sapphire caseback with additional solid caseback, from 1997 onwards with deployant clasp. Also with examples with “E” or Etanche. Dial: lapilated indexes, matching “baton” hands.

It is estimated that 4,000 examples of the reference were produced across all series and metals. The present example Patek Philippe ref. 3970EP-021 from circa 2004 belongs to one of the last examples from the fourth series. Powered by cal. CH 27-70 Q, the caliber is indeed based on the legendary Lemania cal. 2310. Offered in single factory sealed condition, the present specimen of the reference is also accompanied by the full set of accessories. This is perhaps one of the most undervalued Patek Philippe references.