It was in 2009 that Vacheron Constantin decided to create a new minute repeater combining slenderness, a pure sound, aesthetic beauty, reliability and sturdiness. Four years proved necessary to solve this complex equation. While the new Calibre 1731 is barely thicker than its predecessor from 1993 – 3.90 compared with 3.28 mm – due to its impressive 65-hour power reserve, it is nonetheless the thinnest on the market today, having successfully overcome the difficulty of assembling and adjusting parts that have been slimmed down to extremes. Nor are the technical feats confined to the ultra-thin side of its nature, since Calibre 1731 is equipped with a highly ingenious device developed by Vacheron Constantin in 2007 for the 2755 movement – another member of this exclusive family of minute repeater calibres: a flying strike governor. Contrary to classic lever-type governors, this one is completely silent. Its role is to steady the rate at which the hammers strike the gongs. Without a regulator or governor, this musical sequence would take place at the speed of the striking barrel-spring, and would merely produce a rush of indiscernible notes. The device developed by Vacheron Constantin comprises two inertia-blocks or weights designed to act as a brake on the rotating shaft of the governor and thus evening out the energy supplied by the barrel spring. To achieve this, it makes use of two opposing centrifugal and centripetal forces. When the governor spins, the centrifugal force pivots one end of the weights outwards so that the other end presses on the shaft so as to stabilise the rotation speed and thus ensure a steady cadence. Perfectly finished right down to the smallest details, the governor bears Vacheron Constantin’s Maltese Cross emblem, even though the latter cannot be seen from the front of the calibre.