What exactly happened at 23 Quai Conti, in Paris? This is the address of the French Académie Royale des Sciences, which became the Académie des Sciences in 1666. It is here that during the 1750s Ferdinand Berthoud submitted several documents, the first forms of patents on his many inventions, under sealed cover.

At the same time, at the same location, the knight Jean-Charles de Borda also submitted his first works as an engineer, a few years later, embarking on various ships to clarify the calculation of longitude. For these missions, he used measuring instruments created by Berthoud.
 

This collaboration between watchmakers, engineers and sailors forms the essence of Ferdinand Berthoud's period, the famous age of Enlightenment, which he lived through in its entirety. Its purpose was to disseminate and enhance knowledge. Ferdinand Berthoud actively contributed to both missions, as well as writing a large number of articles relating to horology for Diderot and d'Alembert’s Encyclopaedia – the first systematic attempt to provide an exhaustive summary of human knowledge – as well as authoring 11 watchmaking treatises in 30 years.

Berthoud indeed dedicated his entire life as a researcher and watchmaker to the enhancement of knowledge. His countless works on chronometric accuracy and longitude calculation were regarded as authoritative for decades. A master watchmaker at only 26 years of age, he devoted a large part of his work to marine chronometers, essential instruments for accurate measurements related to the calculation of longitude.
 

As early as 1752, the accuracy of these readings was greatly improved thanks to an instrument optimized by the same Jean-Charles de Borda, after whom it was named the Borda circle (also known as a repeating circle). This instrument was designed to measure angular distances by repeating the same observation several times on the circle without returning to zero. Its particularity: the more the measurements it performs are repeated, the smaller its margin of error.

The Borda circle was the essential link that made it possible to pass from the octant (with an accuracy of 150 nautical miles, or more than 270 km) to the sextant (accurate to 0.2 miles, or 370 metres). The Borda circle was conceived as an improvement of the reflecting circle invented in 1752 by Tobias Mayer, a German astronomer known for his lunar tables, which made it possible to determine the position of the Moon and hence longitude in a precise manner.

The FB 1L Chronometer is a model displaying the age and phases of the moon. Combining chronometric precision and astronomical measurement, it associates these two previously dissociated values which jointly made it possible – almost three centuries ago – to achieve more accurate longitude calculations, a quest at the heart of a large number of Ferdinand Berthoud's works. The age and phases of the moon are two separate measurements.

The moon phase is the most common in watchmaking. This is the complication that visually indicates the different lunar cycles. The moon phase is divided into four phases: new moon, first quarter, full moon and last quarter. A lunation or lunar cycle is the time interval between two new moons. A symbolic and aesthetic complication, the moon phase does not, however, offer the accuracy necessary for astronomical use.
 

The age of the moon is a more accurate indicator which counts the number of days since the last new moon. This veritable scientific measuring instrument, coupled with the chronometric measurement of time, made it possible to determine longitude at sea with unparalleled accuracy nearly 270 years ago.

For the first time, the FB 1L collection combines these two instruments: a chronometer and an indicator of the age and phases of the moon within the same model.

The 100% in-house calibre of the Chronomètre FB 1L features an original suspended fusee-and-chain construction. It delivers a constant force to the escapement throughout the operation of movement, from its first turn of the crown to complete winding, thus achieving a 53-hour power reserve.
 

Two versions of the Chronomètre FB 1L are available.

The FB 1L.1 "Near Side of the Moon" model favours a warm and luminous approach reminiscent of the visible face of the Moon and the intensity of the full moon. The piece has a case middle, side elements and crown in 18-carat polished white gold. Its lugs are made of black ceramic.

The FB 1L.4 "Far Side of the Moon" version evokes the dark and mysterious tones of the Moon's hidden face. This time, its white gold case middle is sandblasted and, in place of ceramic, the lugs and side elements are made of dark grey ceramised titanium. On average four times harder than standard titanium, ceramised titanium is part of the sustainability approach adopted in the making of Ferdinand Berthoud creations, which has already led the Manufacture to develop a carburised steel with similar properties.

Each piece will be issued as a numbered ten-piece limited edition