What Is a Watch Power Reserve?

Many mechanical watches will have a power reserve indicator displayed on their dial to eliminate the guesswork of when your watch is going to stop ticking. Each brand designs their power reserve indicators in their own way but the principle remains the same. The visual display shows how much power the watch has left similar to a car’s fuel gauge. The familiar arc is the most commonly seen yet other creative designs have been spotted in a straight line or circle.

The majority of mechanical timepieces will run for approximately 35-48 hours when fully wound. The watch is powered by the ‘reserve’ and when this runs out it is time to rewind your watch. Typically, the standard power reserve is about 2 days however; some can run a lot longer with designs boasting 90 hours, eight days and even over a month of power reserve through multiple mainsprings. Impressive, we know! 


How Does a Power Reserve Work?

When the mainspring is tightly coiled the timepiece is fully wound storing energy to power the watch. As the metal coil starts to unwind, the power reserve starts to decrease, which is usually shown on the dial for reference. Also, the longer the mainspring the more power reserve the watch will have as it takes more time to uncoil.

Those who regular wear their automatic timepiece and are active throughout the day can keep their watch ticking making sure the power reserve indicator does not become empty. Some think it is good practice to wind their watch every night. However, if you have not worn your automatic watch for a few days, which is powered by your movement you can easily spot when you need to fasten it to your wrist again or become more active. Sitting at a desk all day will not power your watch efficiently; therefore a quick walk out of the office may be a good idea. A hand-wound mechanical watch relies on the indicator to tell the wearer when the timepiece needs manually winding.  

The power reserve indicator shows how much power the spring has left and is made possible by adding extra parts to the movement and a differential screw. 


Why Is a Power Reserve Important? 

This function is the perfect way to keep an eye on the power of your watch. It is very helpful to know when your watch needs to be wound and also shows the technicality of your timepiece. Of course, quartz watches do not need a power reserve, as they are battery powered, therefore the presence of the indicator signifies the complexity of the movement. Also, the power reserve is very useful for collectors as some watches will not be worn very often, the owner can easily see if the watch requires winding before being worn that day.