What’s a Breguet Overcoil and why does Rolex care?
When looking at watch specifications there is plenty of watch jargon to confuse anyone who is not well immersed in the watch world. One of the many items that sets Rolex apart from many other manufacturers is that all their watches utilize a Breguet Overcoil in their balance springs. In essence, the balance spring is the regulating heartbeat of a mechanical watch.
Inside the balance wheel, the mechanism that rotates back and forth, is a small, resilient, hairspring tightly coiled together and is what regulates the speed and range with which the balance travels. There are other mechanisms that also regulate the speed and range of the balance wheel, but by and large, it is the smallest and most delicate of springs that the watch’s time keeping ability emanates, similar in this respect to a human heart. Although it appears as a simple spring, it is one of the most engineered aspects of a mechanical wristwatch because it needs to keep its’ resiliency and shape consistent for years at a stretch, is able to withstand lateral shocks, and be able to withstand magnetism. Rolex recognizes the importance of the balance spring and have thus their own in-house balance spring, Parachrom Blu, recognizable by its blue appearance. Click this link for a video depicting how a Parachrom Blu balance spring is made. All modern day Rolex watches have a Parachrom Blu hairspring, and the older one have high quality hairsprings made by Nivarox who manufactures hairsprings for most of the mechanical watch industry.
Aside from Parachrom Blu, Rolex hairsprings also differ from others because they use a Breguet Overcoil. One of the areas in hairsprings that catch watchmaker’s attention is the hairsprings “isochronisms” or movement. When a watch is fully wound, there is more pull on the hairspring causing it to open & close upwards of 300 degrees, known as high amplitude or wide swing of the balance wheel. When the mainspring winds down, there is less pull on the hairspring causing less swing (low amplitude) of the balance wheel. The shorter swing, lower amplitude of the balance wheel will cause the watch to speed up.
In 1795, Louis Breguet invented the Breguet Spiral, otherwise known as the Breguet Overcoil. The Breguet Spiral is essentially a traditional flat hairspring, but the end of the spring bends up back over the top of the spring, anchoring the “pivot point” of the spring closer to it’s center. By having the end of the spring bend up, it essentially tricks the spring into thinking it will always have an equal pull over a broader range of mainspring tension than a flat spring.
A Breguet Overcoil, found in most Rolex watches, combined with the automatic winding mechanism that is present in most Rolex watches, helps to insure greater accuracy and time consistency at irrespective of mainspring tension. The automatic winding mechanism found on most of the Rolex line insures constant mainspring tension, and coupled with the Breguet Overcoil, KIF or Paraflex shock absorbing system in the balance, Rolex’s Parachrom hairspring, and free spring balance with Microstella adjusting screws, all insure that Rolex is one of the most consistent mechanical timekeepers.