The Piaget Protocole Ref. 91545-N (often spelled "Piaget") is a vintage 1970s–1990s ultra-thin luxury dress watch, crafted in 18k solid gold and powered by Piaget’s renowned manual-winding Caliber 9P / 9P2 movement.

• Reference Number. 91545 (an evolution of the classic Ref. 9154). The "-N" suffix typically denotes a factory black dial (Noir) or specific case/bezel configuration. 

• Case Dimensions. Rectangular tank-style profile measuring 25mm wide by 28mm lug-to-lug, with an ultra-slim thickness of roughly 4.6mm to 5mm.

• Material & Gem-Setting. Crafted in solid 18k yellow or white gold. Reference 91545 variants typically feature a factory diamond-set bezel (replacing the signature vertical ribbed bezel of the standard 9154) and sometimes diamond hour markers or pavé accents. 

• Movement. Piaget Caliber 9P (or 9P2), an 18-jewel hand-wound mechanical movement famous for being one of the thinnest mechanical calibers of its era at just 2mm thick. 

• Dial. Minimalist time-only black dial (often crafted from natural black onyx stone or glossy black lacquer) with Dauphine or baton hands and no seconds hand. 

• Crystal & Water Resistance. Scratch-resistant sapphire or mineral crystal. Because of its vintage snap-on caseback, it is not water-resistant.