(IDEX Online) - A unique Patek Philippe watch, the only reference 3448/100 ever known to have been set with sapphire indexes, is to be sold by Phillips Hong Kong, with an estimate in excess of $1.28m.The model was introduced by the Geneva-based company in 1962 as the world's first self-winding perpetual calendar wristwatch. An estimated 568 were produced until the model was discontinued in 1986. Most were made of gold. Only two were made of platinum, of which this is the one. No others are believed to have been set with 11 sapphires and moon phases like the example to be auctioned, known as the Blue Royale (pictured). "Only a prominent collector with high standing with the Stern family, the owners of Patek Philippe, could obtain the utmost privilege of having a special platinum cased reference 3448," said Phillips in a press release.It is describes the watch as "one of the most celebrated reference 3448 to be offered to the public".It is the star lot of The Hong Kong Watch Auction: XIII, which takes place on 27 and 28 November. It is being sold in association with Bacs & Russo, specialists in collectors' watches.