Rare Watches: A unique and historically important 18K gold Patek Philippe perpetual calendar chronograph wristwatch with moon phases and tonneau-shaped case manufactured in 1943 is expected to fetch up to $2.5 million at Christie’s next month. The ultra-rare timepiece is the starring attraction at the famed auction house’s Important Watches sale in Geneva at the Four Seasons Hotel des Bergues on May 10. The watch, ref. 1527, is something of a holy grail for a small, inner circle of long time passionate watch collectors who are aware of its history.

Despite being nearly 70 years old the exquisite timepiece only came to light when first offered at auction 20 years ago, and has since been known as Patek’s "large size, one-off perpetual calendar chronograph” among horology connoisseurs. However, Christie’s notes, the designation is far from doing justice to this “highly important master piece and historically most interesting forerunner of future generations of complicated Patek Philippe wristwatches.” The watch is one of 90 Pateks being offered in the spectacular sale.