The Lange 31 130.039F carries the answer to one of watchmaking's oldest ambitions: a mechanical wristwatch that runs for a full month on a single winding. When A. Lange & Söhne introduced the Lange 31 in 2007, it became the first mechanical wristwatch able to run for 31 days, 744 hours in total, and it paired that endurance with a patented constant-force escapement so that the energy reaching the balance on the last day is the same as on the first. At SIHH 2017 the manufacture presented this White Gold edition with a Grey dial of solid silver, limited to 100 pieces and available only through Lange boutiques. Nothing on the dial announces the scale of the achievement: only a white 31 at the end of the power-reserve indicator and the German word Monatswerk, meaning monthly movement, beneath the outsize date hint at what lies inside. The watch is wound not with the crown but with a dedicated key, a detail that recalls the pocket watches of the nineteenth century and underlines how far this movement departs from the norm of modern wristwatches.
The White Gold case measures 45.9 mm in diameter and 15.9 mm in height, dimensions dictated by the two large mainsprings needed to store a month of energy, yet its proportions remain balanced and its surfaces combine polished and satin finishes in the Lange manner. The Grey dial is made of solid silver and follows a clear, almost architectural layout. Lange's outsize date appears in its double window, with the Monatswerk inscription set discreetly beneath it. A large power-reserve indicator, graduated in days up to the white 31, and a small seconds subdial complete the displays, so the owner can see at a glance how many days of running remain. Faceted White Gold baton markers and rhodium-plated gold hands give the grey surface a quiet, technical elegance. The crown sets the time, and a pusher at 10 o'clock advances the date. On the back, a sapphire crystal reveals the movement and a recess with a square socket for the winding key. A brown alligator strap and a White Gold deployant buckle complete the watch, keeping its appearance as understated as its engineering is ambitious.
The Lange 31's two mainsprings are stacked one above the other, and together they hold enough energy for 744 hours of running. The difficulty with such a large reserve is that a mainspring delivers strong force when it is fully wound and weak force when it is nearly spent, which affects the amplitude of the balance and therefore the rate of the watch. Lange solved this with a constant-force escapement placed between the barrels and the gear train. A remontoir spring supplies the escapement, and every ten seconds a triangular cam on the fourth-wheel arbor and a pivoting lever allow the mainsprings to recharge it with a fresh, identical amount of energy. The result is uniform torque at the balance from the first day to the thirty-first. The movement of 406 parts is wound with a key that fits into the caseback; the key incorporates a backstop ratchet for smooth winding and a torque limiter that prevents overwinding. The workings of the constant-force mechanism can be watched through the sapphire caseback, alongside the German silver plates and hand-engraved balance cock that mark every Lange movement.
A. Lange & Söhne has a long history of practical inventions, but the Lange 31 remains one of its boldest. Before its launch in 2007, mechanical wristwatches typically ran for two or three days, and even the longest-running models measured their autonomy in days rather than weeks. The Lange 31 showed that a month was possible without sacrificing rate stability, and the constant-force principle it introduced became a building block for later Lange watches, including the Zeitwerk, whose jumping numerals depend on a similar mechanism to release energy evenly. The model first appeared in Platinum and Rose Gold, and the Grey-dialled White Gold version of 2017 marked its tenth anniversary with a cooler, more contemporary appearance. More than a decade later, the Lange 31 continues to occupy a special position in the manufacture's catalogue: a watch that addresses a technical question few other makers have even attempted, and answers it in a form that remains wearable and legible every day of the month.
The 130.039F appeals to collectors who value technical ambition above all, and who appreciate a watch whose greatest feature is revealed only on closer acquaintance. It can be worn for a month without winding, set aside for weeks and picked up still running, and wound with a key in a small ritual that connects its owner with the traditions of pocket watchmaking. With 100 pieces made and distribution limited to Lange boutiques, it is also rare. Its White Gold case and Grey dial give it a restrained, modern character that suits business dress, while its size gives it a presence that larger wrists will appreciate. It will interest collectors who own a Zeitwerk and want to understand the constant-force principle in its original form, and those who collect watches that represent a genuine first in horology. For a Lange collection, it provides a statement of engineering confidence; for collectors of German watchmaking, it is one of the clearest demonstrations of what Glashütte can achieve when it sets itself an extraordinary goal.
