The collection of ultra-thin calibres designed in response to the challenge made in1903 by Edmond Jaeger to Jacques-David LeCoultre is among the most extraordinary in watchmaking. It includes several minute repeaters, chronographs, and double complications. But the most famous creation is still the LeCoultre 145 Calibre, produced from 1907 until the 1960s in some 400 copies, only 1.38 mm thick, which made it the flattest mechanism of its time.