Mechanical watches are wind-ups, and as the mainspring winds down, the drop in tension can result in less than consistent chronometric performance, with degraded impulses transmitted to the balance wheel. Clever clockmakers and watchmakers have devised many strategies to manage or alleviate this, and one of the classics is the fusée and chain. Instead of having the mainspring barrel directly geared to the wheel train, variable gearing is achieved by linking it via a chain that is wound around the spiral groove of a conical gear (fusée).
As the mainspring barrel unwinds, more of the chain is unraveled from the fusée, from its narrow tip towards its wider base. In this way, the diminishing torque supplied by the barrel is compensated for by in effect driving the movement through a larger gear – something like downshifting to squeeze out more torque while going up a ramp.
While a clever solution, the fusée and chain drive mechanism is rare today because it is extremely laborious to fabricate, and watches that do feature it, tend to be very classical in design. For those who love a little contrariety in their watches, Zenith has united the fusée and chain with that other archaic contraption that was invented to improve chronometry, the tourbillon, in the breathtakingly modern and athletic Defy El Primero Fusée Tourbillon.
Thoroughly skeletonized, the configuration of the new El Primero 4805 SK manual-wind caliber is neatly ordered with bridges that evoke a sense of high performance from their resemblance to multi-spoke rims on a sportscar – a most fitting chassis for the blitzing 5hz escapement that bears the ‘El Primero’ name. Amidst the contrasting shades of black and grey, the movement’s two star features, the chain and tourbillon cage, are highlighted in blue. While it takes less than 200 parts to construct a three-hand watch, the Primero Fusée Tourbillon’s chain alone consists of 575 individually hand-assembled components – hence its rarity. As for the tourbillon, it is an entirely new construction for Zenith, featuring an off-centered balance wheel that every 60 seconds. On the dial between 4 and 5 o’clock, a power reserve indicator for 50 hours completes the display.
The Defy Fusee Tourbillon is produced in two different editions: in carbon case, limited to 50 pieces; and in platinum case, limited to 10 pieces. The carbon case model also features skeletonised carbon dial and flange, as well as carbon crown and buckle, matched to a black rubber strap with blue stitching; a second rubber strap is also supplied. The strap of the platinum case model is composed of a black rubber core wrapped in black alligator leather.
Manual-wind El Primero 4805 SK, fusée and chain, tourbillon, 5Hz, 50 hours power reserve.
44mm carbon case (50 pieces) or 44mm platinum case (10 pieces), openworked, 10 atm water resistance.
Carbon case model: Black rubber strap, titanium double folding clasp with black carbon head.
Platinum case model: rubber wrapped in black alligator leather, titanium and white gold folding clasp.