pro & con: horizontal vs. vertical coupling - WatchTime

PRO & CON: HORIZONTAL VS. VERTICAL COUPLINGVERTICALJEROME LAMBERTCEO OF JAEGER-LECOULTRE:The Extreme WorldChrono (left) and itsmotor, JLC Caliber752, shown with itsrotor removed. Thevertical coupling(center) has a returnto-zeroheart, achronograph wheeland a copper-coloredfourth wheel.“Jaeger-LeCoultre’s engineers andwatchmakers made reliability and precisiona priority when they developed thenew Caliber 753. For this reason, youwon’t find the conventional toothedwheels of a horizontal coupling mechanismto operate the chronograph’s functions.Instead, you’ll find two disks locatedbetween the fourth wheel and thechronograph’s counters. These diskstransfer energy between those components.They also ensure that the chronographstarts precisely and reliably. Usersimmediately notice the difference becausethe center-mounted seconds handstarts instantly, without delay and withoutthe backward motion often seen inchronographs with horizontal coupling.Other important advantages aren’t noticeableat first glance, but they play animportant role because they enhanceprecision. There are no teeth in the coupling,so the optimum transfer of energyoccurs without loss. This means that thebalance’s amplitude remains constant, regardlessof whether the chronograph isswitched on or not. And our technicianswent one step further: they put two jewelsinto the interior of the coupling mechanism.These rubies reduce friction to anegligibly low value when the chronographis motionless (because the fourthwheel continues to turn constantly). Furthermore,this coupling is extremelyshock-resistant, thus making the watchvery reliable on the wrist. A strong springholds the two disks together firmly whenthe chronograph is running. The diskcoupling embodies precision and reliability.Why isn’t it used more often? Becauseit’s difficult to manufacture and assemble.The utmost meticulousness and precisionare required.”troduced in 2005, has 279 components. PatekPhilippe’s Caliber CH 28-520 IRM Q 24H optsto do without a continuously running secondshand. Thanks to low-friction vertical coupling,this chronograph’s center-mounted secondshand can be allowed to rotate continually. Itcan be started simply by operating the flybackbutton.Another development came in 2006 fromChopard. The L.U.C 10 CF combines verticalfriction coupling and an instantaneous returnto-zeromechanism, along with a small andcontinually running seconds hand that can doa rather nifty trick. If the return-to-zero buttonis activated while the crown is extracted intothe time-setting position, the seconds hand returnsto 12 in the blink of an eye.Vertical coupling does, however, have onedisadvantage. As in an automobile, the couplingoccurs largely out of sight, whereas thehorizontal arrangement is much more attractiveand eye-catching. Once again, it appearsthat even for watch lovers, it is difficult to haveone’s cake and eat it too.■96 WatchTime April 2007