Successor to the reference 2499, Patek Philippe entered a new era of perpetual calendar chronographs with its new reference 3970. Introduced in 1986, the first series of this reference, produced during two years only, featured a snap-on back. After 1988, this timepiece was offered with a screw-down back that would either be full or transparent. According to our preliminary research, it seems that only 3 other such watches have ever been offered at auction and that most probably less than a hundred pieces were ever produced.
Patek Philippe. A rare gold perpetual calendar wristwatch with snap-on back