The true heart of any watch is the power that drives it - without which it stops dead. From Rolex to A. Lange & Söhne, we have summarised all the technical details that you need to know about power reserves and featured some of our favourite watches such as the Tudor North Flag and the IWC Big Pilot's Top Gun. Here's what you need to know about power reserves.
Technically, the power reserve is as old as watchmaking itself. The first watches grew out of the invention of the coiled spring for an energy store, as early as the 15th century. Previous clocks had used simple weights on pulleys, or the flow of water through a water wheel to provide power. Springs were much more effective because they could be condensed into a small space, allowing timekeeping mechanisms to shrink to portable sizes.
"Power reserve", then, refers to the available energy stored in a watch's mainspring. While the watch runs, the spring gradually unwinds, until all the power is spent and the watch stops or is wound up again. Over time, watches have evolved to provide typically around 40-50 hours of power, enough for two days or so. A limiting factor is that if the spring is too powerful at the start, the watch can run fast, as well as becoming too slow as it unwinds - although advances in mechanical watches technology have done a lot to mitigate this "constant force" problem. It's recommended that all manual watches should be wound once a day.
Today, we are not just concerned by the power reserve itself, but by the power reserve indicator, a complication that can be added with a few extra watch parts (usually relying on a differential screw) to display on the dial how much power is left in the spring. Often it is shown as an arc, like a fuel gauge, but it can also appear as a straight line or other creative shapes.
In recent decades, this indicator has become much more frequently incorporated, especially on chronometer men's watches. Not only is it a helpful way to see when the watch needs winding, but it also adds the feeling of a technical upgrade, demonstrating the mechanical complexity of the piece. After all, you would never need a power reserve indicator on a quartz watch.
In addition, many manufacturers are attempting to provide longer and longer power reserves, so the indicator can be a good way of showing off the enhancements. Some will claim that there is not a lot of utility in a longer power reserve in the age of automatic movements, where most mechanical watches no longer require frequent winding. Yet as luxury watch collectors now own an increasing number of watches, self-winding functionality becomes less useful as each watch is worn less often - so the power reserve indicator is still frequently handy.
Even minimalist brands like Nomos now offer power reserve indicators, such as on its gorgeous Tangente. When it comes to showcasing longer reserves, several prestige brands have created timepieces featuring the desirable week-long power reserves (or more) - Jaeger-LeCoultre was among the first in 1919, and still offers 8-day reserves in the Reverso, Master and other collections.
Then there are the truly outstanding entries that often use multiple mainsprings to achieve astonishing lengths of power. The Lange 31 was the first to provide a full month's power reserve in a simple, elegant watch case. It has since been surpassed by the likes of the Hublot Ferrari - the current record holder with a gob-smacking 50 days reserve and a space-age racing car design to match.
Below we consider the power reserves on some of our favourite watches:
In order to honour its ingenious founder, the A. Lange & Söhne manufactory launched the wristwatch in 1815 - the year that Ferdinand A. Lange was born. The watch comes equipped with a prominent “ab/auf” power reserve display at 8 o'clock with a full 72 hour power reserve.SHOP: Lange & Söhne 1815 Auf/Ab
The Big Pilot's 7-day movements are especially impressive because of a secret that lies beneath the practical nature of the dial display: It's actually an 8-day movement. The watch is craftily built to come to a stop after "only" seven days to avoid the accuracy problems that might arise from diminished torque.SHOP: IWC Big Pilot's Top Gun
This special Luminor showcases all the classy design elements that have made these watches so popular - but the real highlight is the in-house movement (P.2002/1) that boasts a GMT function and a whopping 8-day reserve, shown in a nifty linear display on the dial.SHOP: Panerai Luminor 1950 Acciaio
New in 2015, this was Tudor's first in-house watch movement. Everything about it is built for practicality, including the excellent 70-hour power reserve and its simple but legible display - very useful for knowing when to dig out your watch winder.SHOP: Tudor North Flag
This stunner eschews a power reserve indicator in order to create a truly dazzling elegance of stripped-down simplicity. But don't be mistaken: the power reserve is remarkable at over four days (100 hours) thanks to Zenith's phenomenal horological skills deployed on the calibre 6150.SHOP: Zenith Elite 6150
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