Among the many words that people well-versed in technical matters of horology will know, power reserve is one of the most basic, yet tremendously important terms. To sum it up briefly, the movements of all mechanical watches each have corresponding power reserve figures, which indicate how long the watch will run once fully wound. For obvious reasons, this single factor can play a significant role for consumers picking out a new watch, thus motivating those within the industry to push the boundaries of modern watchmaking to achieve amazing feats.
For some, the length of a watch’s power reserve is mistakenly viewed as unimportant, as they own so many watches that when the time comes to wear a watch again, it needs winding. Nevetheless a longer power reserve is appreciated by most seasoned collectors. Especially, those that own perpetual calendars will be able to see the value in a prolonged power reserve, as the consequences of not keeping such a movement constantly wound can be very tiresome. By the same token, it’s not to be understood that the overall power reserve of a movement makes or breaks its desirability, since some movements are already too complex to accommodate additional barrels or larger mainsprings.
Along with power reserves come power reserve indicators – the complication manifestation of the desire to see just how many hours a watch’s reserve has left. Various brands produced prototype pieces featuring this complication, but it truly wasn’t widely available until Jaeger-LeCoultre released their Powermatic, making use of the Cal. 481. This watch featured an indicator located at twelve o’clock that would notify the owner of a low power reserve by displaying the number of hours left in a stark shade of red. Such a complication would then go on to be widely used by a number of different watchmakers in countless different unique applications.
Power reserve indicators have also helped collectors treat their timepieces with better care and ensure that they run accurately and optimally. It has been said before that a watch will only run at a constant, regular rate once at least 30% of its mainspring have been wound. Now with the addition of these helpful indicators, watch owners can easily check to what extent their watch is wound – be it automatic or manually wound.
In recent years, we’ve been treated well by several haute horology manufactures, with the gift of a few pieces boasting astonishing power reserves. One of the most impressive examples of this is the A. Lange & Sohne Lange 31. As the name would suggest, it possesses a 31 day power reserve (!). All of this is made possible by two barrels, each containing an extremely lengthy mainspring, which comes in at 185cm long. Additionally, the German caliber’s patented constant-force escapement ensures power is used sensibly, to always guarantee the validity of the 31 day reserve period. With the aforementioned technical marvels comes a slight caveat, in that the watch measures 46mm wide, which is very large compared to other pieces from Lange. To call this piece exciting would be quite the understatement.
On the considerably more affordable end of the spectrum is another piece that has notably made use of a power reserve indicator in the past – the IWC Big Pilot. Produced in a number of different quiet and more colourful variants, the Big Pilot has now gained somewhat of an iconic status that’s backed by a cult following. Upon first glance, you really can see why. IWC’s Cal. 7-day 51111 beats reliably at the heart of this 46mm behemoth, and the current tension being placed on the mainspring can be viewed effortlessly at three o’clock. Collectors also hold the Big Pilot to a high standard due to the extremely fast time setting, made possible by the large onion crown.