In 2015, Karl-Friedrich Scheufele, the Co-President of Chopard, restructured the eponymous Ferdinand Berthoud name, to honour the Swiss scientist and master-watchmaker. Berthoud (1727-1807), the Horologist-Mechanic by appointment to the French King and Navy, has left behind an exceptional body of work, particularly in the field of sea chronometers.
Berthoud’s royal and navy appointment were earned when his Marine Clocks No. 6 and No. 8 calculated longitudes to within a mere 1/8° margin of error, after being tested at sea for 12 months between 1768 and 1769. The time-measuring instruments created by Ferdinand Berthoud were benchmarks in terms of reliability and precision.
Two hundred and fifty years later, the Ferdinand Berthoud FB 2RE collection created by Karl-Friedrich Scheufele, draws inspiration from Berthoud’s Marine Clock No. 6. Like its predecessor, the FB 2RE has been put through the stringiest quality and performance tests. Like its predecessor, the FB 2RE has earned high praise for its original movement – combining a remontoir d’égalité mechanism with the fusee-and-chain transmission.
“We wanted to develop a genuine wrist chronometer,” says Scheufele, President of Chronométrie Ferdinand Berthoud. “Above and beyond the design, embodying a contemporary expression of Ferdinand Berthoud’s Marine Clock No. 6, the technique is unprecedented: it is an authentic feat, and the combination of fusee-and-chain transmission with a remontoir d’égalité really improves precision.”
The FB 2RE was recently awarded the Chronometry prize at the 2020 edition of the GPHG. In the Chronometry category, the crucial criterion is accuracy. To achieve the highest chronometric performance levels, FB 2RE became the first and only timepiece to combine a fusee-and-chain mechanism with a one-second remontoir d’égalité for its regulation. The mechanism, as a whole, comprises three segments in total which, step by step along the gear train, gradually remove any torque variations liable to affect its accuracy.
The first of these components is the barrel spring. The primary source of energy, the new, aerodynamic, two-spoke variable-inertia balance wheel is fitted with four balance screws. Its large diameter ensures it maintains inertia and stability, while its low frequency of 18,000 vibrations per hour (2.5 Hz) protects the power reserve.
The barrel spring is technically capable of delivering an 80-hour power reserve. However, the Calibre FB-RE.FC only uses 60% (50 hours’ worth) of this energy – the period during which the torque is the most linear. This constant torque is selected by means of a Maltese Cross system; this can be seen on the top of the barrel drum.
In principle, the barrel can rotate up to 8 times, but the Maltese Cross reduces the number of possible rotations to 6, mirrored by the six teeth on its profile. The two smaller indentations on the Maltese Cross prevent the power spring from supplying the gear with too much energy (at the beginning of the power reserve) and too little energy (at the end of the power reserve).
The fusee-and-chain system then provides a second level of constant power. Acting rather like an automatic gearbox, it regulates the torque generated by the barrel, keeping it constant, during the 50-hour power reserve.
Since the torque delivered by the barrel varies depending on how wound up it is, the chain around the fusee is fully wound around the smaller-diameter end of a cone. The barrel spring provides maximum power at this point. As time goes by, this force decreases, with the chain winding around the drum and moving from the smaller-diameter end of the cone to the larger-diameter end. The variation in cone diameter compensates for the reduced torque in the barrel spring. By this stage of the process, the FB 2RE model already has a much higher degree of isochronism than prevailing standards.
The remontoir d’égalité comes next. Positioned at the end of the gear train, it regulates the torque delivered to the escapement. It does so by using a constant force spring. A component very similar to a hairspring, the spring coils and uncoils, always releasing the same quantity of energy, or torque, as it does so.
This remontoir d’égalité operates in conjunction with the escapement wheel. The latter’s rotation spans a 5-fold cycle, following the oscillations of the balance wheel. During the first four oscillations, the remontoire spring uncoils, releasing constant energy. On the 5th oscillation, the triple-shaft stop wheel, which previously prevented the mechanism from coiling back up, is released. This release allows the movement to rewind the remontoire spring, which once again begins to release a constant amount of energy for the next four oscillations, and so on. The entire cycle lasts one second.
This regulated energy then enters the remontoir d’égalité system. This is designed to reduce the small irregularities that occur when the teeth mesh, making the power supplied even more stable – so much so that the energy ultimately supplied to the escapement is almost perfectly constant.
Pursuing the principle dear to the master watchmaker, Ferdinand Berthoud put the Chronomètre FB 2RE.2 through the highest standards of testing by two independent laboratories – first, at the COSC for 15 days, and then, once housed in its case, for a further two days (50-hour power reserve) using the Fleuritest.
The Fleuritest test is conducted by the Fleurier Quality Foundation. This test is one of the most demanding in the watchmaking industry, faithfully reproducing everyday body movements and alternating active and rest periods. During the test, running time variations are analysed using digital cameras. Measurements are taken on a cased movement throughout the entire power-reserve period. These tests are considerably more meaningful in that they are closer to the actual conditions in which clients wear their watches every day.
The result: over the entire duration of the power reserve, the readings are taken show discrepancies of less than 0.5 seconds on average from the benchmark GPS clock optical measurement. For the FB 2RE model, there is thus very little difference in running time between the first and the last minute. This outstanding level of isochronism correlates with the amplitude measurements for the FB 2RE: an average amplitude of 301°, presenting only a very slight variation throughout running time (standard deviation = 2°).
Karl-Friedrich Scheufele, obviously pleased with the achievements of his beloved timepieces, said: “We wish to offer demanding collectors the very best by introducing modern timepieces acknowledged for their reliability and accuracy. In the space of five years, we have received no less than ten international awards, including three at the Grand Prix d’Horlogerie de Genève. This represents recognition for the work accomplished so far by all our teams. It allows us to establish ourselves in the field of Chronometry in a sustainable manner and encourages us to persevere along this path.”