remontoire

In mechanical horology, a remontoire (from the French remonter, meaning 'to wind') is a small secondary source of power, a weight or spring, which runs the timekeeping mechanism and is itself periodically rewound by the timepiece's main power source, such as a mainspring. It was used in a few precision clocks and watches to place the source of power closer to the escapement, thereby increasing the accuracy by evening out variations in drive force caused by unevenness of the friction in the geartrain. In spring-driven precision clocks, a gravity remontoire is sometimes used to replace the uneven force delivered by the mainspring running down by the more constant force of gravity acting on a weight. In turret clocks, it serves to separate the large forces needed to drive the hands from the modest forces needed to drive the escapement which keeps the pendulum swinging. A remontoire should not be confused with a maintaining power spring, which is used only to keep the timepiece going while it is being wound.

==How it works== Remontoires are used because the timekeeping mechanism in clocks and watches, the pendulum or balance wheel, is never isochronous; its rate is affected by changes in the drive force applied to it. In spring-driven timepieces, the drive force declines as the mainspring runs down. In weight-driven clocks the drive force, provided by a weight suspended by a cord, is more constant, but imperfections in the gear train and variations in lubrication also cause small variations. In turret clocks, the large hands, which are attached to the clock's wheel train, are exposed to the weather on the outside of the tower, so winds and accumulations of ice and snow apply disturbing forces to the hands, which are passed on to the wheel train.