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How Automatic Movements Work Their Magic

Mechanical movements aren’t mysteries. Here’s what you need to know about the history of self-winding automatic watch movements and how they work.

It wasn’t that long ago that people paid tolls by handing money to attendants, made phone calls by dialing a number, and created playlists (or mixtapes, if you're of a certain age) by physically transferring their music from records to a tape deck. All this progress is defined by technology’s ability to free us up from the mundane and time-consuming, and it’s a type of progress that has defined innovation for centuries. You can even see this kind of progress in horology if you look back to 1777, when Abraham-Louis Perrelet developed a mechanical watch movement that would eliminate the hassle of winding one’s watch. Emperor's Grand DT 3920 Automatic movements have come a long way from Perrelet's design to the Emperor's Grand DT 3920


As we’ve discussed before, watches with mechanical movements are powered by the uncoiling of their mainspring. This meant that, back in Perrelet’s time, daily winding was an essential part of owning a personal timepiece to retighten the mainspring for another day of timekeeping. Perrelet’s brilliant idea was to reroute the crown-to-mainspring winding mechanism with a slight detour: the rotor. In Perrelet’s pocket watch-based design, the rotor functioned as a weight mounted to the movement in such a way that it revolved as the wearer moved. These revolutions would wind the mainspring, which in turn kept the watch running and eliminated the mundane act of winding your watch before wearing every day. Despite the rotor “replacing” the crown in terms of handing the once-tedious winding process, most automatic movements still allow for “crown winding” as well. Though if you’re like most automatic watch owners, the only time you’re using the crown is to set your time (or dual time) and day/date. It’s no wonder why some watch aficionados take umbrage with people who say, “an automatic watch is different from a mechanical manual-wind watch”—it’s like saying a Tesla isn’t a car simply because of its engine.


While Perrelet’s design was brilliant in its simplicity, it was still designed for pocket watches and, even back in his day, pocket watches weren’t subjected to the level of activity and movement of wristwatches today. That’s because the wristwatch as a concept owes its existence to World War One. Commanders and troops found it difficult to keep reaching for their pocket watches to synchronize battle plans, so a watch movement was engineered to fit into a wrist-sized case and the watch was moved from pocket to wrist. With the war over, the wristwatch was here to stay, and all the beloved designs and innovations of the pocket watch needed to make the leap to the wrist. In 1923, British watchmaker John Harwood reimagined Perrelet’s design so it could fit this new breed of wrist-sized movements. Harwood’s redesign had merit, but it wasn’t without issues—namely, a limited rotor movement which diminished its efficiency in winding the mainspring. Enter an up-and-coming company called Rolex who introduced a reimagined version of Harwood’s reimagined design in 1931 that addressed the rotor’s limited movement and built upon it with their new “Power Reserve” innovation. This feature stored and regulated the mainspring’s power to ensure accurate timekeeping for anywhere from 36 hours to 8 days, even if the watch was in a drawer instead of on a wrist. Given the timeless potential of their movement, Rolex chose to call it “The Perpetual” (a name that is still with the brand today). And while other innovations have come along since, including a rotor that could spin in two directions without unwinding the mainspring, they’re all based on Perrelet’s core design from almost three centuries ago. Special Reserve 657 Signed rotors like on the Special Reserve 657


Fast forward to the current horological landscape, and you can see automatic watches continue to command the watch community’s attention. The innovation has elevated other features as well, with exhibition casebacks becoming a prized feature for admiring precision-crafted elements like skeletonized movements and engraved or signed rotors. They’ve also spawned a successful cottage industry of “watch winders,” computer- and app-controlled devices that mimic the wearer’s wrist motion to keep the rotor spinning when the watch isn’t being worn. Like everything watch-related, these winders range from under $50 to vault-type models that cost more than a house and can handle scores of watches at once. But even without an engineering degree or a down-payment for a watch winder, it’s easy to appreciate just how far Perrelet’s idea has come. Watch lovers everywhere have no problem enjoying the benefits of these advancements while staying true to the soul of Perrelet’s original motivation. You can see it clearly in our Presidia 943—a dual time zone watch that features a day/night indicator, all powered by the increased efficiency of the modern automatic movement. Even more impressive is the fact that this powerful movement fits in a 42mm silhouette, big enough to project a presence yet not so big as to demand it. And with stunning skeletonization and mesmerizing guillochet work, it’s easy to appreciate Perrelet’s legacy in every wind.      


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