Evolution of the original Datograph
The original Datograph (ref. 403, launched 1999) ran the Cal. L951.1, the movement Philippe Dufour famously called the most beautifully finished modern chronograph. In 2012 A. Lange & Söhne updated the Datograph with the L951.6: same architectural beauty, but now with a 60-hour power reserve (versus 36 h on the L951.1) and an added power-reserve indicator at 6 o'clock (the "Up/Down" of the new name). The new ref. 405.031 grew the case from 39 mm to 41 mm to accommodate the slightly larger movement.
What makes it the connoisseur's chronograph
The L951.6 retains every element of what made the L951.1 famous: column-wheel control, lateral clutch via oscillating pinion, flyback reset, instantaneous-jump 30-minute counter, outsize date (the Lange "Großdatum"). On top of these features sits the finishing: hand-bevelled bridges with inward angles, polished sinks for jewels, screwed gold chatons, hand-engraved balance cock, untreated German silver three-quarter plate. The L951.6 adds twin barrels in series for the longer reserve, with constant-force-friendly torque delivery across the run.
Why 18,000 vph?
The L951.x family beats at 2.5 Hz (18,000 vph), the same low rate as a vintage Lemania or Patek manual chrono. Modern chronographs typically run at 4 or 5 Hz; the deliberately slower beat of the Lange has two effects: the chrono seconds hand ticks visibly in 1/5 second steps (instead of sweeping), giving a more deliberate "watchmaker's" feel, and the lower frequency reduces wear on the hand-finished chronograph train. The trade-off is precision: the Datograph chronograph is not a tool watch for sub-second timing, it is a finishing showcase.
Watches using the L951.6
The L951.6 powers the Datograph Up/Down ref. 405.031 (platinum, black dial, 2012-present), and variants in other case materials: ref. 405.035 (pink gold, 2018), and the Datograph Perpetual Tourbillon (which adds a tourbillon and perpetual calendar on the same chronograph base, designated L952.2). The Datograph Up/Down is the standard production reference; the more complex variants share the L951.6 base architecture.
Where it sits
The L951.6 sits at the absolute peak of modern manual-wind chronograph movements alongside the Patek CH 29-535, the Vacheron 1142, and the F.P. Journe Centigraphe. Among these, the L951.6 is uniquely Saxon: untreated German silver, the outsize date, hand-engraved cock, and the deliberate 18,000 vph cadence. Retail for the Datograph Up/Down is around EUR 80,000 in pink gold; secondary market prices are typically 70-90% of retail given Lange production volumes are very low.
