Moser & Cie Streamline Centre Seconds carrying the Centre Seconds Automatic HMC200 Calibre
Also known as a self-winding movement, an automatic movement of a mechanical watch has a mechanism that winds the mainspring by a rotor or oscillating weight. Most rotors pivot freely on their central axle.
Movements of the watch wearer’s wrist will cause the rotor to oscillate and this will in turn wind the mainspring through a series of gears. The accumulated mechanical energy from the coiled mainspring is released as it unwinds. It is the gear train of the movement that transfers this energy to the escapement.
The mainspring of an automatic movement can generally be wound manually as well, similar to a manual-winding movement. A fully-wound mainspring will normally be able to power the movement and allow it to run autonomously for between 36 and 48 hours.
If worn daily, it will not be necessary to wind an automatic movement manually as power is regularly being generated and accumulated automatically as long as wrist movements oscillate the rotor which is typically in the form of a semi-circular weight.
The idea of a self-winding movement arose in the later half of the 18th century. Abraham-Louis Breguet (1747 to 1823) for example, came up with his perpétuelle watch in 1780 using an oscillating weight unlike that of contemporary versions that reacted to movements of the person carrying the pocket watch.
Though an automatic movement does not feature a horological indication, it can be regarded as a complication.