The LANGE 31
SEEN THROUGH A WATCHMAKER’S LOUPE (3 MB)

ENERGY FOR 31 DAYS.

The Lange 31 is yet another example of A. Lange & Söhne’s ability to redefine benchmarks in precision watchmaking. It is the world’s first mechanical wristwatch with a power reserve of 31 days and a constant-force escapement. It is this device that makes it possible for the first time to meaningfully harness such a substantial power reserve. For an entire month, the mechanism assures the highest
level of rate stability and rate accuracy.

The power-reserve indicator

HARMONIOUS BEAUTY.

Thanks to its unmatched autonomy, the LANGE 31 offers a useful benefit – you may forget to wind it once in a while. Because even if you take the watch off, it keeps telling the right time for as long as 31 days. To emphasise this special functionality, the solid-silver dial bears the inscription “Monats-Werk”. Additionally, the power-reserve indicator was accorded ample space on the right-hand side of the solid-silver dial. The patented outsize date on the left-hand side har-moniously balances the face.

The winding key for the LANGE 31

THE KEY TO POWER.

A glance at the back of the watch reveals another construction that is very rare in precision watchmaking – the key-winding mechanism. It was explicitly designed for and matched to this watch. It allows a considerably larger winding transmission ratio than would be possible with a crown. So fewer revolutions are needed, and the energy can be built up faster and more conveniently.

View through the sapphire-crystal caseback

PERFECTION REVEALED THROUGH THE BACK.

The key is inserted through an aperture in the sapphire-crystal case-back. Three seals between the winding mechanism and the case protect the watch against ingress of water up to a pressure of 3 bar. To prevent inadvertent overtightening of the mainsprings, the key fea-tures an integrated torque limiter. An attempt to turn the key further – once the mainspring is fully wound – disengages the triangular tooth-ing of two wheels inside the key and interrupts the flow of power.