Understanding Power Reserve
*Originally published October 2015
In watch lingo, we often talk about the power reserve, sometimes referred to in Swiss watches as Reserve de Marche. Essentially, power reserve indicates how long a mechanical watch can run when fully wound. Every mechanical watch offers a certain amount of power before needing to be wound.
To power a watch, a spring is tightly wound and then placed inside a cylinder or barrel. This is where the energy is stored. The spring releases its tension in a consistent manner, offering constant energy to power the watch at a regular rate. The amount of power a watch has is determined by many factors, including the number of barrels and springs.
Power reserve can differ from watch to watch depending on if the mechanical watch is manually wound (one the wearer must wind himself or herself) or an automatic watch (wherein the rotor of the watch automatically winds during use). The norm on an automatic watch is usually 36 to 42 hours, while a manual wind watch can be equipped with enough power reserve to last for weeks.
Often, the amount of power in the watch is indicated on the dial so that the wearer can see when the watch will need rewinding. That indication can be displayed in a variety of ways. Among them: arched subdials with a hand pointing to an indicator of the remaining power. This is also sometimes achieved using a color palette, such as an arch that displays blue but slowly turns to red as the power runs out. Some brands offer a + or – sign with a hand pointing first to the plus sign when wound and the slowly moving to the minus sign as the power dwindles. There are also linear indications on some watches.
It is important to note that not all watches have visible power reserve indicators. Sometimes, the indication is on the back of the watch and other times there is no indication at all, one just has to intermittently wind the watch, and/or, for some watches – use an automatic winder to keep them powered when not being worn.