130.025

A month of running from a single winding. Two mainspring barrels hold roughly ten times the energy of a normal watch, and because a spring delivers less force as it unwinds, a constant-force escapement between the barrels and the balance meters the power out evenly — otherwise the rate would drift badly across thirty-one days. It is wound with a key rather than a crown.

Reference record

Market value band

$45k – $150k

Notable

• —The remontoir is rewound once a minute, so the escapement receives the same torque on day 31 as on day 1.

What the specification implies

• —The specification calls for key winding. The size of the barrels is why a crown was not practical.

Other Lange 31 references

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