The reference 1518 is one of the most iconic vintage chronographs ever produced by Patek Philippe. First introduced in 1941, the reference 1518 made its mark as the first perpetual calendar chronograph ever produced (and I mean ever). It was only made in 281 examples in yellow gold, rose gold, and stainless steel, which further confirms its rarity. In modern years, it has risen to the top as one of the most collectible vintage Patek Philippe watches making landmark auction results, such as a stainless steel example selling for over CHF 11 million at Phillips in November 2016.