Power Reserve: An Inside Look at What It Is and How It Works

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With so much focus on mechanical watches, you’ve probably heard the term “power reserve.” But what does power reserve really mean and how do watch companies make it happen? Essentially, the power reserve indicates the amount of time the movement can dispense constant energy (the autonomy) before the watch needs to be wound.

Most mechanical watches offer a power reserve of several days on up to eight days (though some brands offer even more than 8 days). Eight days was the target time, as this means the owner of a mechanical hand-wound watch can plan to wind the timepiece once a week (with a single day of safety for the forgetful winder). Of course, should the power run all the way down, the owner can naturally wind it again, but then has to go through the task of resetting the time, date, etc.

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Accomplishing longer power-reserve durations is all about proper springs, gears and cylinders. Essentially, a spring is tightly wound and then placed inside a cylinder. This is where the energy is stored. The spring should release its tension in a consistent manner, offering constant energy to power the watch at a regular rate. Longer reserves mean the caliber has to be larger to make room for a larger mainspring and cylinder, which sometimes translates into a slightly larger watch size.

Two things are worth noting here. One is that winding that spring and placing it into the cylinder is no easy feat. It takes months of training just to properly wind the spring, place it in the cylinder and adjust it so that the force is constant. Additionally, it should be noted that all of these incredible mechanics take place inside a movement that is usually no bigger than the size of a half-dollar coin.

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Most contemporary hand-wound watches feature a power-reserve indicator on the dial. This indicator displays how much energy is left in the movement before it needs to be wound. Some watch brands have made amazing strides in offering creative power-reserve indicators that go above and beyond an arc display on the dial. Either way, the power reserve offers, in a sense, a true symbiotic relationship between the person and the hand-wound watch. The timepiece needs to be wound to continue tracking time, and the wearer has the distinct pleasure of breathing life, so to speak, back into the watch.

Our knowledgeable staff would be happy to demonstrate the power-reserve indications on some of our hand-wound watches. Just stop in any time.

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