How Does an Automatic Movement Work?

Mechanical Energy from Movement

Automatic watches are among the most fascinating forms of mechanical timekeeping. They do not require a battery and, when worn regularly, do not need to be wound by hand every day. The energy is generated by the movement of the wrist—more specifically, by a rotor inside the movement.

This rotor is usually semicircular, mounted on ball bearings, and rotates freely. When the watch moves, the rotor—due to gravity and inertia—does not follow every movement immediately but oscillates within the case. This motion is transmitted to the mainspring via a gear train. The mainspring is wound and stores the energy that subsequently powers the watch.

From the Rotor to the Mainspring

The heart of a mechanical movement is the mainspring. It is housed in the barrel and is wound either by turning the crown or by the automatic winding mechanism. As the mainspring unwinds slowly, it transfers its stored energy to the gear train in a controlled manner.

In many modern automatic movements, the rotor winds the mainspring in both directions. This is referred to as bidirectional winding. A slip clutch prevents the mainspring from being overwound once the watch is already fully wound. This allows an automatic watch to function reliably even when worn daily.

Escapement, Balance Wheel, and Hand Train

If the mainspring were to release its energy unchecked, it would run down in no time. That is why every mechanical movement needs an escapement. It divides the energy into regular pulses. This rhythm is regulated by the balance wheel, which oscillates back and forth at a high frequency together with the balance spring.

The movement of the gear train is ultimately transmitted via the hand train to the hour, minute, and second hands. In this way, stored spring energy is converted into a steady time display.

What does power reserve mean?

The power reserve describes how long a mechanical watch will continue to run when it is fully wound and no longer moved. It can vary greatly depending on the movement. The Sellita SW200-1, which is used in various CiRCULA models, typically offers a power reserve of around 41 hours. The Sellita SW200-2 Power+ offers up to 65 hours, while the La Joux-Perret G100 reaches about 68 hours.

A longer power reserve is particularly convenient when the watch is set aside over the weekend. Ideally, it will stop without requiring the time and date to be reset.

Manual Winding and Second Stop

Many automatic movements can also be wound by hand. This is useful if the watch has not been worn for a long time or needs to be restarted quickly. The mainspring is then wound directly using the crown.

Another practical feature is the second stop. When the crown is pulled out to the time-setting position, the second hand stops. This allows the watch to be set with exceptional precision.

Automatic Watches in Everyday Life

An automatic watch relies on movement. If you wear it regularly, you’ll usually provide it with enough energy. If you wear it only occasionally, a quick manual wind can help. It’s also important not to expose the watch unnecessarily to strong impacts, magnetic fields, or extreme temperatures, since mechanical movements consist of many finely tuned components.

Conclusion

An automatic movement is a small mechanical energy system on the wrist. The rotor, mainspring, gear train, escapement, and balance wheel work together to convert motion into precise timekeeping. It is precisely this visible and tangible mechanics that makes automatic watches so special to this day.