This is a fine Patek Philippe Ref. 3418 Calatrava, also known as the 'Convertible' This reference was believed to only be made in stainless steel for a hand full of years. This rare and unusual model allowed for easy strap/bracelet changes by unscrewing a metal ring fixed to the case back and revealing the lugs within. This piece comes on its original mesh Patek Philippe bracelet that closes like a belt buckle. Just such a cool invention all around. The calatrava style watch is powered by a manual wind caliber 12-400 18 jewel movement. The original black dial is perfect and has gorgeous markers and a subsidiary seconds register at 6 oclock. This watch comes with an Archive from Patek Philippe.