This watch is also known as: Q1646420 164.64.20(Q1646420) 1646420 Limited to 200 Pieces. Sapphire Crystal Caseback.Two years in development this is a stunning addition to the Jaeger lineup. It is the first minute-repeater that is water resistant to 50 meters. It displays its functions through three stunning apertures on the front dial which offer a view into this miniaturized wonder of mechanical engineering. The watch chimes - which are sublime to hear and which were designed in collaboration with the Orchestra Leader Georges Pretre - produce a very sonorous 55 decibels (at two feet away). An incredible 15-day power reserve.