F.P. Journe Octa, Calibre 1300*
The construction of the Octa caliber has less powerful ties with the history of watchmaking than do the remontoir or the resonance models, but it nonetheless symbolizes a horological ideal of giving timekeepers the highest possible degree of precision and autonomy! Within this context, one may mention Jobst Bürgi, who used the remontoir to achieve three months of autonomy for his clock. One might also note the fact that if church clocks are placed so high, in addition to enhancing visibility, it is mostly because it often took an entire month for the driving-weights to drop the full length of their cords. Many systems were invented to increase the duration of run of a watch, meeting with various degrees of success. Given the small volume of a wristwatch, the spring could not be as large as one might wish. Watchmakers therefore discovered the trick of placing an additional wheel inside the customary gear-train so as to extend the duration of its development. Unfortunately, actually using this system, even with a stronger spring, let them to observe that the energy actually reaching the spring remained low. To compensate for this, they fitted a smaller balance using less energy, but which nonetheless lost a considerable amount of stability. It is therefore not unusual to find that some watches able to run for several days have an extremely unpredictable level of precision.
This challenge was a powerful source of motivation! I then imagined that the best and also the most obvious solution to extend the duration of run would be to extend the capacity of the spring development. The difficulty lay in integrating it on the same level as the gear-train and the escapement, due to its size: 1 metre long and 1 millimetre thick. Given the low torque of this spring, I could achieve extremely fast automatic winding (one and a half hours in a Chappuis cyclotest for more than 5 days running).
With the challenge of autonomy now won through this automatic winding calibre, I then knuckled down to the second challenge of inserting various complications into that same movement: power-reserve with large date display, fly-back chronograph with large date display, retrograde annual calendar, etc., while maintaining exactly the same size on all models in the Octa collection.
Three years of research and more than two years of development were required before this automatic winding movement that is unique in the world could be presented to the public
~ François-Paul Journe
Gifted with an exceptional sense of spatial conception indispensable to the construction of such a calibre, François-Paul Journe succeeded in bringing together these two challenges within the automatic winding Octa calibre. Designed in such a way as to maintain a diameter of 30 mm and a thickness of 5.70 mm, whatever complication is incorporated, it establishes itself as the first automatic winding movement with sufficient power-reserve to ensure precision timekeeping during five complete days (120 hours) off the wrist.
Generally speaking, classically built watches with a long power-reserve suffer from the fact that their small balance is sensitive to shocks and other disturbances on the wrist. François-Paul Journe therefore imagined a compact construction featuring a large-size balance (10.1 mm in the Octa calibre) and a high level of inertia, thereby ensuring great stability. This balance with no index is set to oscillate at a frequency of 21,600 vibrations per hour and is dynamically poised in the five positions of the watch. The inertia blocks enable one to advance or delay the balance by changing its effective radius, without interfering with the balance-spring.
This movement provides steady and significant force thanks to a one-metre long spring supplying 850g of torque to the mechanism, with only 25% loss of amplitude when its power-reserve is exhausted. The watch will nonetheless continue to run for around thirty hours after the five days, but without ensuring the same precision timekeeping
Exploded view of Cal. 1300 showing the high capacity barrel
Cal. 1300, rhodium-plated, "fausses côtes" decoration, 22 jewels, straight line lever escapement, monometallic 4-arm balance with 4 timing weights, adjusted to 5 positions, self-compensating free-sprung flat balance-spring, off-center bi-directional 22K "guilloché" gold rotor.
* Technical details from Antiquorum. Other information from Montres Journe catalogue.