Last week we discussed the difference between the Chronograph and the Chronometer.  Both are widely used industry terms that in many respects, Rolex perfected. One of the key components that affect watch accuracy is the balance spring located inside the balance wheel. In essence, the balance wheel is the regulating heartbeat of a mechanical watch.  Even though this might sound like we are getting into the minutiae of watchmaking, the hairspring is critical watch component that Rolex perfected to insure chronometric accuracy.


Like in other industries, namely Apple Computer, Rolex takes watch industry concepts and perfects them such that those concepts can be replicated in the production numbers and consistency that Rolex expects.  This is where Breguet and Rolex meet.  Breguet watches were started in 1795, by Louis Breguet ( and is one of the oldest watch companies in the world.   Louis Breguet invented the Breguet Spiral, now known in the watch industry as the Breguet Overcoil.  The Breguet overcoil is small hairspring where the spring bends up back over the top of the coils, anchoring at the “pivot point” of the spring closer to its center.  By having the end of the spring bend up, the spring is tricked into thinking that it has an equal pull over a broader range of mainspring tension than a traditional flat spring.


Tension on the hairspring and how it breathes (or in watch terms, the “isochronism”) relates directly to timing and accuracy. When a watch’s mainspring is fully wound, there is more pull on the hairspring causing it to open & close spinning the balance wheel upwards of 300 degrees. The amount of mainspring spin is called amplitude and a high amplitude balance has wide swing of the balance wheel. As 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. Conversely, a high amplitude causes the watch to slow, but is more resistant to changes in gravity and g forces.



A Breguet Overcoil is found in most Rolex watches. When combined with the automatic winding mechanism that keep the mainspring wound, the Breguet Overcoil insures 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 combined with Microstella adjusting screws, insure that Rolex is one of the most consistent mechanical timekeepers.


Next week we’ll describe the significance of the “free sprung” balance wheel and Parachrom. Breguet, Paraflex, Kif, and Microstella are all watch components perfected by Rolex to help guarantee chronometer certification accuracy.

– Sheldon Smith