A remontoir d’égalité is a small secondary power store between a watch’s mainspring-driven train and its escapement. The train periodically rewinds the remontoir’s spring; a release mechanism then feeds that stored energy to the escapement. By buffering changes in mainspring force, it aims to make the regulator less dependent on how fully wound the watch is. It can help address one source of rate variation, but it does not guarantee greater accuracy in every watch.
How a remontoir d’égalité works
The mainspring’s force changes as it unwinds. A remontoir inserts a brief energy-storage and release cycle between the barrel and escapement, so the escapement receives energy from the secondary spring rather than directly tracking every change at the barrel.
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- The barrel drives the train. The mainspring turns the barrel, which transmits energy through the watch’s gear train.
- The train rewinds the remontoir. A portion of the train’s motion winds a small secondary, or equalizing, spring.
- A mechanism meters the stored energy. A locking and release arrangement lets that spring deliver energy to the escapement at set intervals.
- The cycle repeats. After release, the train rewinds the secondary spring for the next interval.
In the F.P. Journe Tourbillon Souverain example, a secondary wheel sits on a lever. The lever stops the principal wheel, which carries the seconds hand and transmits energy from the barrel, while the auxiliary spring powers the escapement. The secondary wheel releases once per second, then the principal wheel rewinds the auxiliary spring. Journe compares the action to a dam controlling water flow to a turbine. This one-second cadence describes that example, not every remontoir design. F.P. Journe’s Tourbillon Souverain description explains the arrangement.
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As a mainspring unwinds, its torque changes. That variation can affect balance amplitude; because a balance spring is not perfectly isochronous at every amplitude, the watch’s rate may also change. A remontoir aims to reduce the escapement’s dependence on the barrel’s changing force by supplying energy from a periodically rewound secondary spring. The principle and its limitations are described by Horopedia’s overview of constant-force mechanisms.
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The remontoir is not lossless: friction, the quality of pivots and contact surfaces, and the calibration of the secondary spring all matter. If losses are high or the spring is poorly calibrated, they can reduce or undermine the intended benefit. A remontoir is therefore a design strategy, not a standalone promise of improved timekeeping.
How it differs from a tourbillon
A remontoir and a tourbillon address different possible causes of rate variation. The remontoir seeks to reduce the effect of changing mainspring force on the escapement. A tourbillon rotates the regulator to compensate for gravity’s influence in vertical positions. One mechanism is not a substitute for the other, and neither guarantees accuracy by itself. Horopedia distinguishes these functions.
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Where the mechanism came from—and why it remains relevant
F.P. Journe’s historical account associates early remontoirs d’égalité with watchmakers led by Jost Bürgi (1552–1632), describing their purpose as delivering constant force to the regulating assembly whether the mainspring was fully wound or nearly unwound. This is the manufacturer’s historical account, not a conclusive claim of priority. Journe says he incorporated a remontoir in a pocket watch made between 1983 and 1984, then in a Sympathique clock in 1987 and later pieces. The maker’s account provides those dates.
Journe also says constant-force mechanisms were widely used in 19th-century building clocks, partly to isolate the time mechanism from the load of external hands. Their complexity and laborious construction contributed to their near-abandonment during the 20th century, although some makers continued using them. The company presents its Tourbillon Souverain as the first wristwatch form in its collection to use the device. These are manufacturer-reported historical claims. F.P. Journe’s history and model description sets out that account.
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Modern wristwatch example: the Chronomètre à Résonance
In an announcement dated 28 April 2020, F.P. Journe described a Chronomètre à Résonance in which one barrel powers two movements through a differential. Each secondary gear train has its own one-second remontoir. The company said the remontoirs supply linear force to the escapements and assure isochronism for 28 hours. That duration is the maker’s claim for this model and arrangement, not a general performance figure for remontoirs. Read the company’s 2020 announcement.
The announcement states: “Each secondary gear train is equipped with a Remont oir d’Egalité of a frequency of 1 second.” The release does not name an individual speaker; the statement is attributable to F.P. Journe’s official announcement. The example shows why the mechanism remains relevant in specialized high horology, but the available sources do not establish a universal, independently measured accuracy gain.
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What to compare between remontoir watches
When evaluating two actual remontoir-equipped movements, compare details the makers disclose rather than assuming the shared name means identical operation.
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- Release interval: Establish how often the secondary spring releases. A one-second interval appears in the cited Journe examples, but is not universal.
- Mechanism layout: Look at the form and placement of the secondary spring and the locking and release parts.
- Claimed equalizing duration: Note the period over which the maker says the mechanism supplies equalized force, and keep the claim tied to that specific movement.
- Power reserve: Compare the movement’s stated reserve separately from any claimed period of constant force; the two are not interchangeable measures.
- Evidence of performance: Check whether the maker publishes independent comparative rate testing. The cited sources document examples, not a controlled comparison across brands.
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