It was Vasco da Gama's drive to discover new worlds and his unswerving courage that inspired Montblanc’s watchmakers to new horological achievements. The Tourbillon Cylindrique NightSky Geosphères is more than just an intricate watch, it is an eye-catcher with the 47 mm case and the large sophisticated dial. The following functions are provided by the hand-wound calibre MB M68.40: a triple time zone with local time displayed in the form of hours and minutes; the continually running and independently adjustable display for the home time is presented on a three-dimensional twelve-hour compass rose at “6 o’clock”; and a pair of globes depict the World´s 24 time zones in the Northern and Southern Hemisphere, along with the passage of the days and nights.
The two miniature globes illustrate the passage of the days and nights in the northern and southern hemispheres. Engraving and miniature painting on these two halved balls indicate in relief the outlines of the continents, their borders and the oceans that separate them. Their elaborately crafted and finely detailed design also shows the circles of latitude and longitude. The two globes are motionlessly affixed to the movement, while two 24-hour worldtime indicator discs with the day/night display make one revolution per day around them. The disc for the northern hemisphere turns clockwise; its counterpart for the southern hemisphere rotates anticlockwise. This arrangement enables the watch’s wearer to view, in the course of a single day, the sunlit halves of the two globes and the halves that are currently turned away from the sun. With the aid of the meridians of longitude, the viewer can read the current time in any desired part of the world by following the 24-hour world-time display on the two discs.
Montblanc developed the 281-part hand-wound Calibre MB M68.40 featuring a 91-part tourbillon mechanism with a cylindrical hairspring which guarantees a power reserve of 48 hours. The balance-wheel frequency is 18,000 vibrations per hour. The moment of inertia, thanks to the 14.5 mm balance wheel, is 59 mg.cm². Today, very few Manufactures still have the necessary expertise to produce balance-wheels and hairsprings. It was only possible for Montblanc to develop a cylindrical balance-spring for the Tourbillon Cylindrique NightSky Geosphères because of the capacity to manufacture both components in the Montblanc Manufacture. The challenges for Montblanc’s watchmakers were to miniaturise this type of balance-spring and to install it in the tourbillon mechanism of a wristwatch.
The 16¾-line Montblanc calibre MB M68.40 is embedded in a 47-mm-diameter and 15.38-mm-height white gold case. The alligator-skin strapis attached to the watch by four rounded horns that have been thoroughly and lavishly polished by hand. The names of 24 cities in the Northern Hemisphere and another two dozen metropolises in the Southern Hemisphere are engraved along with the matching time zones on the back of the case. The limited numbers from 01/18 to 18/18 are engraved on the sapphire crystal in the back of the case.
