Sotheby’s Important Watches auction on Oct. 5 will be led by a timepiece many consider to be one of the most important watches ever made: Patek Philippe’s Sky Moon Tourbillon 5002.

This “white whale” of Patek models is expected to fetch between $1.3-$2.6 million at the Hong Kong-based sale, which will also feature over 200 timepieces—including a double-signed Patek Philippe Tiffany & Co.-blue Nautilus and rare examples of Rolex sport models. “The offering in this sale encompasses all the wonders of horology, curated not only for seasoned collectors, but catering to the demands of young watch lovers—particularly those aged forty and under, who accounted for 67% of total bidders in our April sale,” said Joey Luk, head of watches for Sotheby’s in Asia, in a statement.

The Sky Moon Tourbillon Ref. 5002 was Patek Philippe’s most complicated wristwatch at launch and is the brand’s first creation that features a double dial. The timepiece boasts twelve complications on two dials, a mechanical feat that was inspired by the Star Calibre 2000 pocket watch featuring a complex sky-chart, which Patek Philippe miniaturized it to fit onto a wristwatch.