百達翡麗，鉑金萬年曆計時腕錶，配月相、24小時及閏年顯示，型號3970EP，1999年製，附百達翡麗後補證書、額外底蓋、盒子及外包裝

In 1986, Patek Philippe launched a new generation of the perpetual calendar chronograph wristwatch, designated reference 3970, replacing the hugely successful reference 2499 in production in four different series from 1951 to 1985. The main difference in the movement was the arrival of the new Lemania based ébauche which replaced the Valjoux movement used for the previous 50 years. Starting with movement number 875'000, the first series of reference 3970 was produced with a solid snap on back, comprising approximately 100 examples. The second series introduced a solid screw back, designated reference 3970E (E for étanche, French for waterproof). A small number of watches from both series were also available with a sapphire crystal back, designated reference 3971E.
In 1989, a third series of ref. 3970 was launched, fitted with a solid screw back as well as an additional sapphire crystal display screw back. Reference 3970 was discontinued in 2004 and replaced by reference 5970.

While production of the reference 3970⁄3971 may have ended only 16 years ago, these modern yet classic perpetual calendar chronographs have become a must-have for the discerning collector of complicated wristwatches.