The present lot was previously sold by Antiquorum, New York, May 26, 2004, lot 159. Ref. 3970 (1986-2005) This Reference was introduced, for Patek Philippe's 150th anniversary, to replace Ref. 2499, which was produced from 1951 to 1985. The Series: As a general rule, the Ref. 3970 was produced in 18K white, rose, yellow gold, and platinum, with the latter being the rarest. The first series featured a 36 mm. case with snap-on case back. This model 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 screw back. After the second series, Patek Philippe introduced the Ref. 3971, similar in design to the 3970 but with a sapphire crystal display screw back. The third series, Ref. 3970E (E stands for etanche which means waterproof), was housed in the same 36 mm. case. Because of numerous special order requests, Patek Philippe took the opportunity to feature the 3970E with both a solid gold screw back and a sapphire crystal display screw back. It is probably the most common of the three series. The Dials When Ref. 3970 was first introduced, Patek Philippe would occasionally accommodate a special customer?s request to order a custom dial. This resulted in some interesting and extremely rare case/dial combinations. The first generation dial of these references was offered in two-tone silver with bâton markers. The dials may be variously described as satiné silver or opaline silver. The second generation dial is silver (not two-tone as in the first generation) and features the same bâton markers, but the font used on the dial is slightly different, and the date wheel is sans 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. 3970?s in 18K yellow gold with silver diamond dials; such watches are extremely rare. The Hands The earlier models (first generation) had leaf hands, whereas later models (second generation) had bâton hands. One extremely rare variation on the Ref. 3970 has been seen with dauphine hands. The Movements The Ref. 3970 was fitted with the 27-70 caliber throughout its entire production. The number system changed during the mid 1990s, from a six digit serial number beginning with 875 to a seven digit serial number beginning with 304. This Ref. was no longer featured in the catalogues as of 2005.