Q: Why do mechanical watches have longer power reserves?
Recent mechanical watches use lightweight silicon in their escapements, which improves friction loss and tends to extend the power reserve. Power reserves can also be extended by increasing the length of the mainspring housed in the barrel or by reducing the vibration frequency.
2025/6/20 update
A: Silicon is used in the escapement to reduce friction loss.
It is now difficult to extend the performance of mechanical watches. That was the opinion 20 years ago. However, modern mechanical watches have been successfully improved in magnetic resistance and extended in power reserve without compromising performance. It is not difficult to increase the magnetic resistance of mechanical watches by using magnetically resistant materials. So how do they extend the power reserve?
Since 2000, manufacturers have begun using silicon, a material that is resistant to magnetism, in escapements and other components. This material is also lightweight. As a result, movements equipped with silicon escapements have improved friction loss in the escapement, making it possible to extend the power reserve.
A recent approach that has become prominent is to make it possible to fit a longer mainspring by thinning the wall of the barrel that houses the mainspring that powers the watch, or by narrowing the arbour around which the mainspring is wound. Previously, the volume of the mainspring that could be housed in the barrel was theoretically determined.
However, advances in mainspring materials have made it possible to pack more spring into the watch, and as a result, some movements have been able to nearly double their power reserve.
The Caliber 888.5 used in the Longines Legend Diver extends its power reserve by incorporating many of the same measures mentioned above, including the adoption of a silicon escapement and a reduced vibration frequency. The original frequency of 28,800 vph was reduced to 25,200 vph, and the balance spring and super-fast escapement parts were replaced with silicon, resulting in a power reserve of approximately 72 hours, roughly double the previous model. Automatic (Caliber 888.5). 21 jewels. 25,200 vph. Power reserve of approximately 72 hours. Stainless steel case (39mm diameter, 12.70mm thick). Water resistant to 300m. Each is priced at 388,300 yen (tax included).
The approach of lowering the vibration frequency is also effective
Another approach is to slow down the watch's vibration frequency. For example, if the frequency is reduced from 28,800 vibrations per hour to 21,600 vibrations per hour, the energy can be allocated to the power reserve. However, since slowing down the frequency reduces the watch's accuracy when in use, this method is only applicable to a limited number of movements. Longines' Cal. L. 888.5 is a good example of a watch that utilizes these methods, including a silicon escapement and a change in frequency.
So, is there a way to improve accuracy without having the watch readjusted? The most effective way is to change the orientation of the watch when storing it. The accuracy of a mechanical watch can change significantly depending on how it is placed. This is called "positional error." Positional error can be troublesome, but depending on how you use it, it can be a useful way to adjust the accuracy throughout the day.
