A. Lange & Sohne Lange 31 ’Monats-Work’ 18kt White Gold Limited 100 Pieces 130.039 with a Constant-Force Escapement and Double Stacked Mainspring Barrels. The 45.9mm diameter solid three-body case, curved lugs, and concave cupped bezel, are polished. The dial is rhodium silver with applied faceted 18k white gold hour markers, around a perimeter minute scale. It has polished white gold epee hands, and there is a recessed silver subsidiary running small seconds dial at 6 o’clock. A silver-rimmed double-window quick set Big date aperture is at 10 o’clock, and it’s operated by a rectangular button on the case edge at 10 o’clock. There is a railroad-style scale at 3 o’clock for the 31-day, 744-hour power reserve - the first to last an entire month. Fitted on an alligator leather strap with a unique 18kt White Gold foldover deployant buckle.

The dial of the Lange 31 is made of sterling silver with a rhodium finish, and the overall layout is quite minimalistic. Extending from the center are the white gold sword hands that reach to the short white gold batons applied to the dial as the hour indices. The A. Lange & Söhne logo is printed at the top of the dial, and under the outsized date are the words “Monats-Work,” meaning months of work in German, giving meaning to the 31-day power reserve indicator. That sizeable power reserve indicator encompasses most of the right side of the dial, and the ending 0 and markings are printed in red, signifying that the power is completely drained at that point. Overall the design is unique for Lange but very authentic for the brand. It’s water resistant to 30 meters/100 feet, and the 15.9mm thick case, dial, and movement are all signed.

This A. Lange & Sohne Lange 31 130.025 has a mechanical manual winding Lange caliber L034.1 movement. It’s three-quarter plate with Cotes de Geneve ribbing, and it’s constructed with 62 jewels including 61 rubies and one transparent sapphire. It has 406 components, blued screws, three screwed gold chatons, a whiplash precision index adjuster on a hand-engraved balance cock, and two stacked mainspring barrels with each accommodating an 1850mm spring (10 times longer than a conventional wristwatch). At full tension the twin barrels store over 3 Joules of energy, and the constant force escapement provides continuous energy from the mainspring without any loss of accuracy. The mechanism oscillates at a frequency of 21,600 vph (3 Hz).

The Lange Caliber L034.1 is a mechanical engineering masterpiece. The immaculately finished caliber consists of a total of 406 parts and is fitted with 62 jewels throughout the movement. Peeking beneath the three-quarter plate finished with the Glashütte ribbing, one can see a small portion of the two massive spring barrels that power this timepiece. Filling those two spring barrels is 1850mm in length of spring, which is about ten times longer than the average wristwatch. That is so unconventional that winding this movement cannot be done through the crown. The owner needs to insert a key into the watch’s caseback and wind it manually to get the whole 744 hours of power reserve.

This brings up the second and possibly more intriguing aspect of this movement: how the timepiece regulates all that power. A patented constant force mechanism builds up the energy in increments over every minute. Then it continuously releases the power into the balance wheel, which beats at 21,600 vph and allows for even and accurate timekeeping throughout the entire 31 days. Insanely impressive given that those mainsprings store over 3 Joules of energy when fully wound. All this and the brand ensures each and every component is finished in typical Lange fashion, with many finishing techniques and even some surprises like a clear sapphire jewel set into the constant force mechanism. This masterpiece features a patented constant-force escapement. The double stacked mainspring barrels, each with an impressive 185cm long spring, store the energy. A constant-force escapement situated between the mainspring-barrels and the going-train assures that the balance receives an identical amount of energy every ten seconds, regardless of the state of wind of the springs.

It has an , and a scratch resistant sapphire crystal. There is a screw down winding crown, and an exhibition sapphire display case back secured with 6 screws, and engraved with "A. LANGE & SOHNE – GLASHUTTE," a serial number, and several hallmarks. There is a circular keyhole for the winding key system on the solid part of the case back that’s sealed with 3 gaskets insuring water resistance. It is not wound by the crown, but by a winding key that fits into a matching aperture on the case. The provided key has a built-in torque sensor, once the watch is almost fully wound the key senses the increase in tension & will disengage the ratchet key.

The LANGE 31 is the world’s first mechanical wristwatch with a power reserve of 31 days and a patented constant-force escapement. The white-gold model has a grey dial made of solid silver. Limited to 100 pieces, this is boutique exclusive limited edition.

Reference No. 130.039F