Calibre PP 350 (and the similar PP I-350) is an automatic watch movement from Patek Philippe. It was the industry's first peripheral rotor automatic movement, used from 1970 through 1985.
Cal. 350 was a highly innovative movement on its introduction, with a bi-directional peripheral rotor for automatic winding and back-mounted stem and crown. This technology had been patented in 1955 by Paul Gosteli but never produced. However, this unconventional winding system proved unreliable, even after a 1979 re-design with uni-directional winding, the Cal. I-350. This too proved problematic and the entire series was retired by 1985.
Cal. 350 featured a free-sprung Gyromax balance, 28 jewels, and earned the Geneva Seal.
Cal. 350 has a poor reputation today, but its problems are likely over-stated. The short life was likely due in major part to the unconventional location of the crown on the back of the watch, an arrangement that did not match most watch models. Patek Philippe also found success with Cal. 240, still in production today, Cal. 315, and Cal. 27-460.
Calibre I-350 (for “Improved”) was introduced in 1979 to fix the issues associated with Cal. 350. The major difference is the replacement of the bi-directional winding system with a uni-directional gear. About 10,000 I-350 movements were built and used by 1985.
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