A. Lange & Söhne’s mechanical digital watch- original Lange Zeitwerk, a classic watch combines a groundbreaking design.
The watch cuts a striking figure. Its most dramatic feature is the winged German silver time bridge that extends over the dial to frame the digital hour and minutes displays as well as the small seconds subdial, effectively unifying all these elements. Besides its aesthetic appeal, this bridge is also a functional part of the movement: it holds the arbor for the two minute disks with an unusual colorless jewel and is secured visibly to the mainplate by a screw.
In conjunction with the two digital displays this creates a harmoniously balanced image. The Zeitwerk is immediately recognizable as a Lange product, with its up and down indications on the power display and unique shape of the hands. The shape of the case reflects typical Lange styling, and even the digital displays have a familiar look: they use the same type of numerals as do the large date indications on many other Lange watches. Lange dispensed with the usual bar between the first and second digits of the display, which is an appealing aesthetic touch.
In that watch, the hours appear as Roman numerals in the first window while the second window, showing the minutes, advances only every five minutes . The minute indication on the Zeitwerk is much more precise and involves a shift every minute. This “jumping” minute indication has presented a massive challenge for other watch companies that have attempted it. 
The outer minute disk advances by one step while a fly vane decelerates it. This component — shaped like a tiny revolving door — creates air resistance to slow the movement but still allows the disk to advance within a fraction of a second each minute. A. Lange & Söhne used the ingenious constant-force mechanism to solve the problem of decreasing rate precision due to energy required for advancing the disks. This refined yet complicated technology was used in a slightly different way in the Lange 31. It ensures that a constant amount of torque is delivered to the balance wheel independent of the state of the mainspring. Lange produces its own hairsprings in addition to the spring for the constant-force escapement, bringing the number of components in the Zeitwerk to an impressive 388.
The movement was adjusted as carefully as it was decorated. Measurements on the timing machine showed a minimal positional error of only four seconds. The Zeitwerk ran slightly ahead in all positions, and the average deviation was quite low, at only +1.5 seconds per day. Moreover, even after the watch had been worn under real conditions for three weeks, the watch showed exactly the same results. It takes some time to become accustomed to reading the disks within the windows; a standard digital display reads much differently.
The barely audible click that occurs when the minute disks advance sounds like a tiny lock snapping into place, and is only slightly louder than the ticking of the Lange movement. Less pleasing is the warning sound we all know from mechanical clocks, which is caused by the minute disk being slightly offset downwards about six seconds before it jumps. The case, with its satin-finish center section and narrowing lugs, is the picture of reserved elegance. The slightly raised caseback has a concave edge that makes the watch appear flatter than it actually is. Every surface boasts excellent polishing and finishing.
The hand-stitched crocodile strap has fully turned edges and an attractively large pattern. The distinctly shaped pronged buckle might have been more carefully polished on its inner surface, but the clever strap design ensures that the clasp lies snugly against the inner wrist and the strap bends very little. Fortunately, the rather sharp edges of the clasp are not very noticeable when wearing the watch. Despite its large size the Zeitwerk lies comfortably on the wrist.
