A remontoir, from the French remonter, to wind, is a small second spring placed between the mainspring and the escapement. The mainspring’s job is reduced to rewinding that little spring at fixed intervals, every few seconds or so, and the little spring is what actually drives the escapement. Because the small spring is always rewound before it can run down very far, the escapement gets nearly the same push every time, from the first hour to the last. It is one of the oldest and cleverest answers to the central problem of mechanical timekeeping: a mainspring that cannot help pushing unevenly. (It belongs to the wider family of constant-force mechanisms.)
A spring remontoire, diagrammed for the 1911 Encyclopaedia Britannica. The principle is centuries old. Photo: Wikimedia Commons, public domain.
The problem it solves
A mainspring is strongest fully wound and weakest nearly spent, so the force reaching the escapement fades over the life of the wind. That fading shows up as rate variation: the watch keeps slightly different time on day one than on day three. Watchmakers call the goal isochronism, the same rate regardless of power state, and the remontoir chases it directly. Instead of asking the escapement to tolerate the mainspring’s mood swings, it inserts a buffer. The intermediate spring delivers its energy in a repeating saw-tooth: a tiny dip as it relaxes, then a rewind back to full, over and over, so the average force at the escapement stays effectively constant. When the barrel no longer has enough torque left to rewind the little spring, the watch simply stops, which is the honest version of running down.
How it works
The remontoir spring looks like a small balance spring and sits in the gear train just before the escapement. A triggering mechanism, often tied to the fourth wheel or the seconds, releases and rewinds it at fixed intervals. Those intervals can be anywhere from one second to a minute. Short intervals are the more impressive engineering: rewinding every second means the force barely varies at all, and as a bonus the seconds hand can be made to jump once per second, a deadbeat seconds, which is why several remontoir watches have them. The trade is complexity. A remontoir adds parts, friction, and adjustment headaches in exactly the part of the movement where precision matters most, which is why it stayed rare for so long.
From Harrison to the wrist
The principle goes back to marine chronometers. John Harrison used remontoire-style maintaining power in his sea clocks, where constant force was not a luxury but a navigational necessity. It took centuries to shrink the idea to the wrist. The modern revival belongs to independent watchmaking: F.P. Journe’s Tourbillon Souverain Remontoir d’Égalité pairs a remontoir with a tourbillon, Grönefeld’s 1941 Remontoire rewinds its little spring every eight seconds, and A. Lange & Söhne’s Lange 31 stretches the interval to a full minute while running a 31-day power reserve off a key-wound barrel. Each one is a small production, fiddly to make and expensive to buy, which is the remontoir’s permanent condition: the best solution hardly anyone uses.
A tourbillon up close. Remontoirs often keep it company in high-end constant-force calibers. Photo: Wikimedia Commons, CC BY-SA 2.0.
Why it matters
The remontoir matters because it is the most direct possible attack on the mechanical watch’s oldest flaw. The fusee evened out torque with a cone and chain. Long power reserves brute-force the problem with more spring. The remontoir just refuses to let the escapement see the problem at all. It will never be common, and it does not need to be. Its job is to show what the ceiling looks like: this is how steady a mechanical watch can be pushed, by the people stubborn enough to build a second spring just to protect the first one’s feelings.
Thanks for reading this.
