Examining this watch is like taking a trip into the past to see the development of French ideas of improving timekeeping. It was in this watch that several of these ideas were implemented for the first time. Ferdinand Berthoud mentions the watch for the first time in his introduction to the "Traité des Horloges Marines", pu-blished in 1773: "In 1765 I began making a watch very different from the ones before, and in which I incorporated all the devices used in my Horloges Marines. The movement was done this very year." In his introduction to "De la mesure du temps ou Supplément au raité des horloges", published in 1787, Ferdinand Berthoud noted: "This Montre de poche à Longitude, that I have just sold to HRH The Prince of Asturias, has been made under my direction by my nephew Louis Berthoud, since that time, this maker follows the principles of construction found in my marine clocks and watches, pocket watches beating seconds, for compensation for heat and cold, employing the detached escapement and isochronous balance springs. The precision of his handwork that he gives to all his products, combined with the principles he follows, allows him to achieve in these watches a very great accuracy." Finally, this watch is mentioned for the last time in the appendix to Supplément au Traité des Montres a Longitude, published in 1807: "In 1765 I designed the longitude pocket watch and a blanc of the movement was made. Since then the watch has remained untouched as I was too busy with other works, and anyway, the movement was not that well finished. Eventually, I had the watch finished again by a good worker: it was completed in 1785 for HRH The Prince of Asturias". Thus, Ferdinand Berthoud’s first longitude watch, the first French spring detent watch, which he began in 1765, was in fact made in 1785 by his nephew Louis Berthoud. The watch was first used by Ferdinand, who intended to use it in tests, and was eventually sold in 1787 to The Prince of Asturias, the future King Charles IV. Furthermore, it is the only watch made by Louis Berthoud under the direction of and to a design of his uncle and the only one to carry two signatures of the men who were pivotal in developing French precision horology. The watch was lost and its where-abouts unknown until 1995, when the mo-vement surfaced, remarkably well preserved, in Calcutta. The upgrades mentioned in our condition report refer to the application of jewels to the balance for the friction rollers. Louis Berthoud after 1792 was known to replace some of the friction rollers for jewels in his watches brought to him for repair. The same must have been practiced by Louis Berthoud’s Spanish pupils, whom he trained in the art of marine chronometry for the Spanish government. One of them, Cayetano Sanchez, who stayed with Louis from 1789 until 1793, upon returning to Spain was put in charge of organizing the manufacture of chronometers at the Spanish Royal Observatory at San Fernando. He died in 1800. Two others were sent to Louis Berthoud in 1801 for training; upon their return in 1806, they were put in charge of manufacturing chronometers in the Royal Observatory. When the watch was brought to them for regular cleaning, they upgraded it as their master, Louis Berthoud, had taught them to do. For Ferdinand Berthoud, the watch must have been very special. It was after the fruit of his research into such areas as escapement, minimization of friction, temperature compensation, and the isochronism of the balance. In his "De la mesure du temps ou Supplément au Traité des horloges marines et Essai sur l’horlogerie", Paris, 1789, Berthoud described the watch in the most minute detail, including drawings of the layout and the escapement. Louis Berthoud certainly considered the watch exceptional. It was his first portable precision timekeeper. The same year that he finished it, Louis Berthoud began working on his own design of portable precision timekeepers, which, as the next lot confirms, became the cornerstone in French manufacturing of portable precision horology. It would appear that it was his work on this watch that induced him to do so. Charles IV King of Spain It is not surprising that this watch was ordered by the Prince of Asturias, the future Charles IV. The King had a consi-derable collection of watches, of which he was very fond. He is said to have been able to take a watch apart and put it back together. And the watch still ran ! L. Constant, in "The Private Life of Napoleon Bonaparte", wrote: "…Thus King Charles, freed from a throne which he had always regarded as a heavy burden, could hereafter give himself up unreservedly in reti-rement to his favorite pursuits. In all the world he cared only for the Prince de la Paix, confes-sors, watches, and music; and the throne was nothing to him. …I spoke above of the fondness of the King of Spain for watches. I have been told that while at Fontainebleau, he had half a dozen of his watches worn by his valet de chambre, and wore as many himself, giving as a reason that pocket watches lose time by not being carried." Literature: Ferdinand Berthoud, "De la mesure du temps ou Supplément au Traité des horloges marines et à l’Essai sur l’horlogerie", Paris, 1789, Plate V. J.-C. Sabrier, "La Longitude en mer à l’heure de Louis Berthoud et de Henri Motel", Antiquorum Editions, Geneva, 1993, p. 422. The watch is illustrated and described in Antiquarian Horology, Winter 1997, pp. 522-534.