The Evolution Of Patek Philippe World Time Watches 1937 1940 1954 Ref. 515 HU Ref. 1415/1 HU Ref. 2523 Cal.10''' HU Cal.13-130 HU Cal.12-120 HU 1939 1948 1966 Ref. 1415 Ref. 1415 Ref. 2523-1 Cal.12''' HU Cal.12-120 HU Cal.12-120 HU