With virtually any brand with high-end ambitions having at least one in its collection and also becoming more and more affordable (as low as 400 USD on some Chinese models), the tourbillon lost its aura of mystique and unobtainable. In other words it lost its position as a "grail" watch feature.
Fortunately, it seems to be another complication capable of achieving the "grail" feature status: the Constant Force Remontoir (CFR).
While the tourbillon ensure positional isochronism, the CFR ensures isochronism against the non-constant power of the mainspring.
Basically, the CFR is a small spring placed somewhere within the gear train (usually between second wheel and escape wheel) that regulates the power received from the mainspring to charge the balance wheel. The CFR works somehow in a similar manner with the escapement - it has its own escape levers that allows only a small and constant amount of power to be released to the balance wheel. In some recent solutions, the CFR was integrated with the main escape wheel and/or lever and in this case the system is called Constant Force Escapement (CFE) - about this I will talk later.
The CFR concept is not new and it was used in past in chronometers and high end pocket watches. I first encountered the term in the book of George Danies where he prise it as an elegant solution to address the non-constant power source isochronous problem. An alternative solution to this problem is the "chain and fusee" but with the disadvantage of being much bigger and complex (more parts) than the CFR.
The CFR though elegant, has its own drawbacks: is difficult to build (high tolerances) and more fragile than the "chain and fusee". Moreover, many have questioned the necessity of both on regulating the power as modern mainsprings are much smoother than old ones and the lever escapement is pretty good in itself with dealing with such power variations.
Anyhow, the same things were said about the tourbillon: is complex, fragile and not necessary increases precision on a wristwatch. This did not stop the tourbillon from becoming a market success perhaps because it is so visually pleasing.
CFR is less aesthetic than the tourbillon and I believe this is the main reason why it finds its way so late in modern wrist timepieces. Thus, for now, the offering of CFRs is limited and they are very expensive. One can still count on fingers the available CFR watches. Let's see them:
1. FP Journe Chronometre Optimum with a CFR beats beats once per second (dead beat second hand visible on the back) and a frictionless escapement.
2. Tensus from Heritage Watch Manufacture (Karsten Frässdorf). This watch has so many interesting chronometric features that I will not discuss them here. Interesting to note that in the Tensus the CFR is integrated within the escapement so KF calls it an CFE - the advantage is it regulates the force for each beat rather than for each second:
3. Lange 31 - the only wrist watch that can run continuously for one month. in this case the CFR is a necessity rather than a "nice to have" as the mainspring is huge and gives big power differences during the 31 days of running. Interesting to note the key necessary to wind the watch (it would take too long to wind by crown)
4. Lang & Heyne offers some amazing pieces with their CFR Caliber V:
5. Girrard Peregraux Constant Escapement with a very original design taking advantage of multi-stable states of a buckled silicon spring. We will see if this invention will pass the test of time:
6. Christophe Claret Kantharos - perhaps the most interesting piece as the CFR is integrated into a rather utilitarian caliber - automatic, chronograph with a striking complication. It demonstrate the CFR as a mature technology for wristwatches ready to go mainstream.
So, here you have it. CFR is an old solution for improving precision that found its way in some very cutting edge modern watches.
The questions for forum are:
1. Which CFR watch do you like the most and why?
2. Any other example of CFR watch that worth mentioning?
3. Most important: does CFR for wristwatches has chances to follow the tourbillon path or die in its infancy?