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A remontoir d'égalité — commonly shortened to remontoir — is a mechanism interposed between the mainspring and the escapement whose purpose is to deliver a constant, regulated force to the oscillator regardless of fluctuations in the mainspring's torque output. Whereas a standard movement transmits the mainspring's energy directly through the gear train to the escapement, a remontoir stores energy in a small secondary spring that is wound at regular intervals by the main gear train and then releases at a consistent force level. The oscillator sees only this secondary spring, not the mainspring directly.
The practical benefit is significant. A mainspring delivers diminishing torque as it unwinds, which introduces the isochronism errors that make many watches run faster when freshly wound than when nearly run down. A remontoir eliminates this by ensuring the impulse delivered to the balance wheel is the same at every stage of the power reserve. The result, in theory, is improved rate stability across the full winding cycle.
Remontoirs appear in some of the most technically ambitious watches in horology. F.P. Journe builds a remontoir into his Tourbillon Souverain and Chronomètre Souverain, releasing every second. George Daniels incorporated the concept into several pocket watches. Greubel Forsey uses a remontoir in combination with its double tourbillon. The mechanism is complex and space-intensive, which is why it remains confined to high complications and independent watchmakers willing to accept the engineering challenge. When executed well, it represents one of the most principled solutions to the central problem of mechanical timekeeping.
The terms are closely related and sometimes used interchangeably, but a constant force escapement specifically refers to a mechanism integrated into the escapement itself — typically a small spring on the pallet fork or escape wheel that is rewound with each tooth release. A remontoir is usually a larger mechanism in the gear train that rewinds at less frequent intervals. Both aim to deliver constant force; the remontoir operates at a coarser level.
It depends on the design. F.P. Journe's remontoir releases every second, which means the secondary spring is rewound 86,400 times per day. Some remontoirs release every few seconds or with each turn of a specific wheel. The more frequent the release, the more consistent the force delivered — but also the more complex and wear-intensive the mechanism.
It should contribute to more consistent rate across the power reserve, which improves practical accuracy. However, it adds friction and complexity, and a poorly executed remontoir can introduce more variation than it removes. In the hands of the best independent watchmakers, it demonstrably improves rate stability — but it is not a shortcut to accuracy on its own.
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