You might wonder, if LeCoultre was able to make such a thin caliber in 1907, why anyone would make a fuss about Piaget’s achievement of a hand-wound movement only 2mm thick with the 9P, in 1957. The answer is that while making a pocket watch movement very thin is surely a huge challenge, making a wristwatch movement that thin is exponentially more difficult. The much smaller size of wristwatch movements means even tighter tolerances and it also means a much smaller mainspring, so there’s less power to work with, and everything has to be made to an extremely high standard of precision. HODINKEE editors have seen extra-thin watchmaking being done in locations as varied as several factories in the Vallée de Joux, as well as in the Seiko watch studio in Shiojiri where the Credor ultra-thin watches are assembled, and true ultra thin watchmaking is treated everywhere it’s practiced as a separate specialization, which requires its own special training – it’s almost as if it’s a complication on its own.

Which is why, when Piaget introduced its caliber 9P at Basel in 1957, it caused such a huge sensation.