An automatic/self-winding movement is powered by a thin spiral torsion spring, called the mainspring, which is housed in an end barrel inside the movement. The energy produced from the wound spring drives the movement functions. An automatic watch has a weighted rotor mounted on a pivot to the back of the movement, and the rotor is connect to the mainspring through a series of gears. The natural motion of the wearers wrist will cause the rotor to spin, which in turn will automatically wind the mainspring.
Please note: An automatic winding watch which has completely wound-down or is at the end of its power reserve requires manual winding. Manually winding an automatic watch ensures that the watch is at full power-reserve when first worn, and as long as the watch is in motion tafter it will remain fully wound, ensuring that when the watch is removed it will run the specificed power-reserve duration.
English
