Spero Lucem La Jonction – Tourbillon Jumping Hours and Retrograde Minutes

From the sand banks of the Middle Ages to the market gardens of the 19th century, Geneva’s Jonction district has been associated with fertile ground. It gets its name from the junction of the Arve and Rhone rivers. The exact address of this geographical point is 3, Sentier des Saules. In the 20th century the Jonction’s proximity to hydraulic power produced by the two rivers, attracted the renowned Geneva instrument maker, SIP, which became the cradle of the precision-tools industry. Nearby, the Nationale Company became renowned for its luxury mechanisms.

In its endeavours to honour Geneva, Spero Lucem has given the name of La Jonction to its second new model for 2013. As the last word in micro-mechanical science, this timepiece is at the confluence of a trio of major complications that exemplify the finest Swiss watchmaking and are a pleasure to observe.

La Jonction is a concentration of watchmaking skills. Its flying tourbillon with gold adjustment screws in the balance-wheel is a faithful interpretation of Abraham-Louis Breguet’s celebrated invention. The tourbillon’s revival in the 1990s never ceases to inspire the best contemporary watchmakers because of the dexterity and capabilities that it demands. Here the tourbillon is associated with mechanisms for jumping hours on a disc and a retrograde minutes hand. The refinement of the classic-looking La Jonction model is evident in the hand finishing of every detail. The dial is divided into two distinct sections. The tourbillon can be seen at 6 o’clock rotating every minute to keep the rate perfectly steady. The clarity of the radiant dial makes it easy to read the fine numerals of the jumping hours appearing in the aperture.

The tourbillon cage is inspired by the head of the pastoral key appearing on the Geneva coat-of-arms. The sunburst snailed engraving on the dial echoes the feathers of the imperial eagle’s wing. On the back of La Jonction, the eagle’s crown forms the bridge of the centrifugal governor.

To the right of the hours aperture, the minutes arc completes the allegory of time. A complex system, known as retrograde minutes, fitted with a hold and release mechanism, makes a single hand add up the minutes like a gauge. The hand doesn’t go all the way around: as soon as it reaches the end of its arc it flies back to the start in a flash. It’s a feast for the eyes of those mad about mechanical watches.

Technical details

Movement
La Jonction Calibre SL2
– One-minute flying tourbillon
– Balance-wheel with gold adjustment screws
– Jumping hours on a disc
– Retrograde minutes hand
– Power-reserve indicator on the bridge side
– Manually wound

Dimensions and performance
– Casing-up diameter: 34.10 mm
– Movement height: 7.80 mm
– Movement height with hands: 9.71 mm
– Number of parts: 257
– Number of jewels and anti-shock systems: 33 jewels
– Power reserve: 97-100 hours
– Balance frequency: 21,600 vibrations per hour (3 Hertz)

Technical
– Height of the hour numerals: 2.35 mm
– Retrograde minutes arc: 120°
– Tourbillon diameter: 13.60 mm
– Arc of the power-reserve indicator: 72°
– Torque: 860 g/mm
– Barrel rotations: 15
– One revolution of the barrel in 8 hours
– Escape-wheel: 15 teeth
– Balance inertia: 10 g/cm2

Operation
– Two-position crown
– Position 1: winding
– Position 2 (crown out): setting the time
– Travel of the winding stem: 0.85 mm

Tourbillon
– Flying tourbillion, 13.60 mm diameter, beryllium-copper balance with gold adjustment screws
– Tourbillon bridge, mirror polished by hand in the traditional way, on a zinc base.
– 159 parts, all finished by hand, make up the tourbillon.

Jumping hours
– Jumping hours in an aperture at 11 o’clock.
– Digital indication that does away with hands. At the end of each hour, the hour numeral is instantly replaced by the next.
– The jumping hours appear a disc rotating under the dial, providing a mechanically driven digital indication.

Retrograde minutes
– Retrograde system, 60 minutes
– Gold minutes hand as a stylised infinity symbol

Hand finish
– All the steel parts are straight grained with polished chamfers.
– The brass bridges are chamfered, circular grained, decorated and surfaced before being coloured.
– Every operation is carried out in strict compliance with the requirements of the Geneva hallmark.

Case
– Materials: gold or titanium. 42 mm diameter, 12.55 mm height
– Machining tool: numerically controlled, 5 axes
– Finish: circular brushed caseband, hand-polished bezel and back, brushed lugs with polished flanks

Dial
– Material: gold
– Finishes: sanded and galvanised black

Strap
– Material: crocodile leather, large scales above; small scales underneath.
– Finish: hand-sewn.
– Buckle: titanium, logo in 5N gold.

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