Watch Terminology Dictionary

A mechanism with two mainsprings. It was once used to drive chronographs and independent second hands, but is now mainly used to extend the power reserve or increase the torque of the mainspring. A prime example of the former is IWC's 52000 series, while examples of the latter are Omega's caliber 8500 series and Cartier's 1904MC series. The advantage is that a larger mainspring capacity can be housed in a smaller movement. The disadvantage, however, is that the gear train must be smaller. While not widely used in the past, its high space-saving nature and the advantage of being less likely to cause the balance wheel to lose amplitude have earned it favor, and in recent years it has been increasingly adopted in core movements.