The large, precise, hand-wound movements in the 59000-calibre family have an 8-day power reserve, but could theoretically run for 9 days. The extra day in reserve ensures that the movement maintains as constant a driving torque as possible and continues to run precisely. The movement is stopped mechanically before the reduced torque can cause it to start running inaccurately. This also means that the owner can safely wind the watch once a week. The indexless balance has a frequency of 4 hertz (28,800 beats per hour) and, together with the Breguet spring bent into shape in accordance with age-old watchmaking tradition, helps to make the watch exceptionally accurate.