A one of kind Patek Philippe 1518 is up for auction at Christie’s, the 1518 was the first perpetual chronograph manufactured. The 1518 was produced from 1941-1952, only 281 watches were created. The model up for auction was sold in 1943 based on the archival extract provided by Patek Philippe. The unique feature of this watch is it is the only 1518 to have the wording, Calendrier Perpetuel on the patina dial. At the time, this watch cost approximately $1,000. Today this watch is expected to bring anywhere from $570,000 to $975,000.

http://www.hodinkee.com/blog/on-the-block-patek-philippe-1518-calendrier-perpetuel-christies