Patek Philippe Calatrava 3520
Patek Philippe had created dozens of variations on the classic Calatrava design by the 1970's, but the 1973 introduction of Ref. 3520 had a novel design: Some models featured Clous de Paris guilloche decorating the bezel. This would become a signature feature of the Calatrava, overshadowing the classic Ref. 96 look in the minds of many enthusiasts. This was paired with a simple round case and straight lugs, a design which some earlier Calatrava models had used.
Ref. 3520 is a simple watch with just hour and minute hands. It uses the hand-wound Cal. 177. The dial originally featured simple markers but Roman numerals and Arabic numerals were used as well.
A larger, automatic version, Ref. 3590 was introduced shortly after, along with a quartz model, Ref. 3722. Today, Ref. 5119 (small seconds), Ref. 5120 (no seconds), and Ref. 7119 (ladies) inherit the Clous de Paris look.