Reference 2508 is one of the most desirable Calatrava iterations Patek Philippe ever produced and, along with reference 565, among the very first waterproof ones. Introduced in 1950 and kept in production until the early 1960s, it distinguished itself twice over: a new take on the traditional Calatrava look, and central seconds in an era when that was still rare.
Roughly 1,200 examples were made across three metals: about 800 in yellow gold, 240 in pink gold, and only around 150 in steel.
Steel is the rarest by output and by far the most desirable.