The Ref. 3970 is considered a classic by collectors, like its predecessors Ref. 1518, Ref. 2499, and Ref. 2499/100.
The Series: Three series may be distinguished in the production of Ref. 3970. A ?series? is defined by variations in case designs or features, whereas dials are designated as ?first generation?, ?second generation?, and so on. As a rule, the Ref. 3970 was produced in 18K white, rose, yellow gold, and platinum, with platinum being the rarest variation, therefore always the most sought-after. The first series of Ref. 3970 featured a 36 mm. case with a snapon case back. This model should be considered extremely rare since it was produced in fewer than 100 examples from 1986. The second series of Ref. 3970 also featured the 36 mm. case, but with a solid screwed back. After the second series, Patek Philippe introduced the Ref. 3971, similar in design to the 3970 but with a sapphire crystal display screwed back. The company also received many special order requests to make the 3970 with an additional sapphire crystal display screwed back. The third series, Ref. 3970E (E stands for étanche, meaning waterproof), was housed in the same 36 mm. case. Due to many special requests, Patek Philippe supplied the 3970E with both a solid gold screwed back and a sapphire crystal display screw back. This is probably the most common of the three series. The earliest examples of the first series of Ref. 3970/2 with 36 mm. case had a gold bracelet fixed to the traditional case; later the bracelet was integrated. A few early Ref. 3970/2 watches were sold with a solid snap back. Such watches are exceptionally rare. The remainder of Ref. 3970/2 have the more common screw back. Finally, in the first and second series, the watches were generally sold with tang buckles, whereas in the third series (Ref. 3970E), after 1997, a deployant buckle was added.
Dials: when Ref. 3970 was first introduced, Patek Philippe occasionally granted a special customer?s request for a custom dial. This resulted in some interesting and extremely rare case/dial combinations. As time went on, it became increasingly rare for the company to accommodate requests for special dials. Consequently, any interesting or unusual dial variation can add tremendously to the value of the watch.
The two generations of standard dials: The first generation dial was offered in subtle two-tone silver with baton markers. Generally, the printing is lighter on earlier dials, and the numbers on the date wheel feature a serif font. The dials may be described as satiné or opaline silver. The second generation dial is silver (not two-tone like the first generation) and has the same baton markers, but the font used on the dial is slightly different, and the date wheel is without serif. The third generation dial is silver, but with darker printing and triangular markers. The platinum and 18K white gold Ref. 3970s were also available with a black dial, and/or diamond markers or white gold/platinum indices (the latter being much rarer). There are a very small number of Ref. 3970s in 18K yellow gold with silver diamond-set dials; such watches are extremely rare. Patek is also known to have made diamond dials in both salmon and white. It is very rare to find a Ref. 3970 with a custom dial.
Hands: The earlier models (first generation) had leaf hands, whereas later models (second generation) had baton hands. It is not known when this change took place. One extremely rare variation has been seen with luminous dauphine hands.
Movements: Ref. 3970 was fitted with the 27-70 caliber through its entire production. Although there are no variations in the caliber itself, the number system did change in the mid 1990s, going from a six-digit serial number beginning with 875 to a seven digit serial number beginning with 304. In 2005, Ref. 5970 replaced Ref. 3970 in the Patek Philippe catalogue.