Montblanc Chronograph Automatic Open Date (104981)

With the ExoTourbillon Rattrapante, the Montblanc Collection Villeret 1858 presents a new timepiece and a horological world premiere. This model offers an unprecedented combination of numerous horological complications: a large balance positioned outside the tourbillon's rotating cage, a chronograph with split-second function, and a three-dimensional regulator dial in gold and grand feu enamel.
Unlike a conventional tourbillon, Montblanc's ExoTourbillon frees the large screw balance from the burden of the rotating cage. Rather than offering a mere chronograph, the new model encases a split-second chronograph with two column-wheels and a classical double clamp. And instead of an ordinary face, the watch's dial is a three-dimensional arena of massive gold and grand feu enamel. This combination of the traditional watchmaker's art and trailblazing innovations comes with an 18 karat white gold case and a regulator dial.
Rattrapante or split-second chronographs justifiably rank among the so-called grandes complications. It's quite likely that the first split-second chronograph was built by the Swiss watchmaker Louis-Frederic Perrelet, the grandson of the watchmaker Abraham-Louis Perrelet of Neuchâtel, who invented automatic winding by means of an oscillating weight in the 1770s.
Ordinary chronographs define the upper limit of so-called "everyday" or "petites complications", but split-second chronographs are grandes complications in the truest sense of the phrase. Extraordinary mechanical complexity and almost 70% more components than for a conventional chronograph mechanism are needed to enable them to perform their useful function, i.e. momentarily halting the split-second hand to indicate an intervening interval without interrupting the ongoing measurement of an elapsing interval by the chronograph's elapsed-second hand per se.
The chronograph's functions are visible through the sapphire crystal in the back of the case: one can see the column-wheel (which controls the basic chronographic functions), the split-second column-wheel (which opens and closes the brake-clamps of the split-second wheel), and the manually bevelled steel levers (which, when the corresponding buttons are pressed, transfer their commands to the column-wheels and thence to the gear-coupling, the zero-return hearts and the brake-clamps). Also visible are the slender, elegantly curved, steel springs that press the rattrapante-clamps against the split-second wheel when the rattrapante button at "2 o'clock" is pressed to allow the user to read the duration of an intervening interval. When this button is pressed again, the clamps spread apart and the zero-return heart automatically returns the split-second wheel to synchrony with the chronograph-wheel so that the split-second hand re-joins the chronograph's elapsed-seconds hand and resumes running in unison with it.
Tourbillon escapements are another specialty of the master watchmakers at the Montblanc Manufacture in Villeret.
The tourbillon was invented more than two centuries ago to counteract the disturbing influence which the Earth's gravitation exerts on the steady oscillations of a watch's balance. A tourbillon rotates the entire escapement around the balance's staff at an unvarying speed, thus compensating for rate errors caused by slight eccentricities in the centre of gravity of the balance and hairspring when the watch is in a vertical position.
With the Tourbillon Bi-Cylindrique, the Montblanc Collection Villeret 1858 again debuted an exclusive new timepiece that differs in several respects from everything previously seen in haute horlogerie. This is the first wristwatch with a tourbillon escapement that ticks with two cylindrical hairsprings that have identical torques but unequal diameters and that are concentrically positioned one inside the other. This unprecedented device makes it a pleasure to reveal the mechanisms and the mode of functioning of the legendary heures mysterieuses display.
With the ExoTourbillon, Montblanc has further optimized the ingenious tourbillon mechanism and made it even more attractive. The Ancient Greek prefix "exo" means "outside". This exteriority is meant in two senses for the ExoTourbillon. First, the rotating cage and the escapement are positioned outside the movement's plate per se and are located, so to speak, alongside the movement. Second, the balance is installed outside the rotating cage and oscillates on a different plane. Timepieces in the Montblanc Collection Villeret 1858 reap significant benefits from this novel repositioning. The uncommonly large and massy balance would have required a larger rotating cage if it had been mounted inside a conventional tourbillon construction. But the ExoTourbillon cage has a smaller diameter than the balance and rotates beneath the gleaming golden screw balance.
The balance is borne between two bridges, the upper of which has a looped shape that recalls a horizontal figure-of-eight as the symbol of infinity. The tourbillon rotates in a two-point bearing at the foot of the axis.
Another exclusive feature of the ExoTourbillon is the speed of its rotations, each of which requires four minutes. Conventional tourbillons typically complete one rotation per minute. Slowing the speed of the rotations enhances the observer's pleasure and requires less energy from the barrel, but produces the same compensating effect as a speedier tourbillon. The hairspring with an upward Phillips curvature at its outer end oscillates at the traditional pace of 18,000 semi-oscillations per hour (2.5 hertz) and thus enables this chronograph to measure elapsed intervals to the nearest fifth of a second.
Reducing the tourbillon's rotational speed by 75% yields considerable energy savings. The rotating cage is smaller and has less mass, so its rotary motion requires less energy as well. Furthermore, the balance is freed from the weight of the rotating cage, which yields a further reduction in its energy requirements. Montblanc's innovative device requires more than 30% less energy than conventional constructions, and this is advantageous for the functioning of the split-second chronograph. Another essential benefit ensues from separating the balance and the rotating cage: the accuracy of the balance's amplitude is improved because the balance is not influenced by the inertia of the cage.
Due to the ExoTourbillon's innovative configuration and despite the greater mechanical complexity of the split-second chronograph, the rattrapante can function more precisely. It can at the same time rely on the same barrel and the same power reserve as the basic chronograph movement. These advantages would not have been possible in a chronograph that does not rely on the patented ExoTourbillon construction.  
The ExoTourbillon Rattrapante shows the ordinary time of day or night as do regulator clocks, the faces of which give the main stage to the minute-hand, while the hour-hand slowly circles its subdial at "6 o'clock". This is an allusion to the historical long-case regulator clocks that kept time more than two centuries ago. This display is augmented on the dial of the ExoTourbillon split-second chronograph by an indicator for the time in a second zone. The smaller dial at "6 o'clock" accordingly bears two hour-hands: the upper and skeletonised hand shows the hour in the current local time zone, while its underlying and greyish companion indicates the hour in one's home zone. These two hands sweep their circles one above the other and indicate the same hour when the wearer is in his home time zone. But when the watch's owner travels to another time zone, he presses the button at the "8" to reset the local-time hour-hand in hourly increments. The little 24-hour display, which keeps the user informed about the current time in his home zone, is located at the right beside the subdial for the hours.
 
The dial of this timepiece is not dial, but offers an elaborate three-dimensional structure. A circular aperture at 12 o'clock shows the ExoTourbillon.
The ExoTourbillon is positioned outside the movement plate per se, so the partially openwork dial and the transparent pane of sapphire crystal in the back of the case offer deep and rewarding insights. The regulator dial is a multipart construction of massive gold. Its primary surface is plated with rhodium and adorned with a graine decor, the area around the tourbillon is recessed slightly. It is surrounded by a flange (rehaut) that's calibrated with a readily legible fifth-of-a-second scale for the chronograph and that simultaneously shows the sequential minutes. All other scales are crafted as grand feu enamel appliques. The applied scale for the continually running second-hand is at the "9", the chronograph's counter for thirty elapsed minutes is at the "3", and the bipartite enamel applique at the "6" hosts the hours display in two time zones and the 24-hour display for the home time.
The circular gold case measures 47 mm in diameter, is polished to a high-gloss finish, and bears a highly domed sapphire crystal with vertically descending flanks (forme chevee) that optimally complements the distinctive shape of the case. The screwed back includes a sapphire crystal viewing window through which one can admire the full beauty of the elaborate mechanism. The edges of the components are bevelled, their surfaces are brushed, and their flanks bear fine, elongated embellishments.
This new collector's item from the Montblanc Collection Villeret 1858 is available only in a strictly limited edition of eighteen watches, each with an 18 karat white gold case.
The watch is affixed to a black alligator-leather wristband equipped with a pronged buckle made of 18 karat white gold.