What Is an Automatic Movement? How It Works

An automatic movement is a watch mechanism that winds itself through the natural movements of the wrist, with no need for a battery or daily manual winding. In practice, an oscillating weight, known as a rotor, spins with every movement of the arm and transfers this energy to a spring that then powers the entire mechanism. This principle, nearly a century after its earliest versions, is the one found in our automatic watches.

The central role of the oscillating rotor

The rotor is arguably the most iconic element of an automatic movement. It is a half-moon-shaped weight, mounted on a pivoting axis, positioned at the back of the movement. Every movement of the wrist sets this rotor swinging, turning freely in either direction. This rotational motion is transmitted, through a series of gears, to a spring known as the mainspring. It is this spring that stores the energy produced by the rotor's oscillations, rather like a mechanical battery recharging over the course of the day. The more regularly the watch is worn, the more charged the spring stays, which is why an automatic watch worn daily generally runs without interruption.

From the spring to the movement of the hands

Once the mainspring is charged, the energy it holds is released gradually through a set of gears that distribute it throughout the movement. This energy powers, in particular, the escapement, a mechanism that regulates the release of energy with extreme regularity, in small successive impulses. It is this escapement, paired with the balance wheel oscillating at a constant frequency, that gives the automatic movement its characteristic beat and steady operation. The regulated energy is then transmitted to the hour, minute, and sometimes second gear trains, which turn the hands with precision. This whole process runs continuously, as long as the watch receives enough motion to keep the spring charged.

A power reserve for periods of stillness

Even when not worn, an automatic watch generally continues to run for a certain time, thanks to the energy stored in the mainspring from previous wear. This duration, known as the power reserve, varies by calibre, but it explains why an automatic watch left on a table overnight often still shows the correct time the next morning. If the power reserve is fully depleted, the watch simply stops; it then only needs to be put back on the wrist, or wound manually if the movement allows it, to resume normal operation.

Maintenance planned over time

Like any mechanism made up of many moving parts, an automatic movement requires regular servicing to keep running with precision over the years. A periodic service checks the lubrication of the gears, the condition of the spring, and the overall accuracy of the movement. This is where the repair service offered by Maison MONTIGNAC takes on its full meaning: it accompanies the watch well beyond the moment of purchase, so it keeps its accuracy despite the natural wear of its components.

Understanding how an automatic movement works helps one better appreciate the work involved in assembling it in the workshop. To go further, our chronograph watches add extra timekeeping functions to this same principle, while discover our full range of watches remains the best way to compare the different calibres the house has to offer.