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COVERSTORY
 If
we are becoming blasé today regarding tourbillons, we should remember their very recent history in production wristwatches: Even today it is rare to see
a tourbillon wristwatch with additional complications – and they do not come much rarer than...
The Remontoir d´Egalité
For
a watch or clock to tell the time accurately, we need two important mechanisms: one to provide power to run the movement and hands, and a second (the escapement)
to distribute that power in very precisely measured intervals. With a tower or tall pendulum clock, weights were pulled up and provided power to run the movement.
The constant period of the pendulum regulated the escapement, which released power at precise intervals. Because the weight does not change on its downward path,
the flow of power to the escapement and movement was very smooth. Well, it would have been if the inefficiencies in the drive train caused by poorly shaped tooth
profiles in the gears, sloppy tolerances between parts and even the effect of strong wind on the hands of tower clocks did not all play a detrimental role, and
they all did.
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The
remontoir was designed to combat these problems. This clever complication was invented by Jobst Bürgi in the fifteenth century to smooth out fluctuations in
the power transmission to the escapement because of inefficiencies in the gear train. As gear tooth profiles became more refined and gears and parts were made to
tighter tolerances, this became less of an issue. However, in the nineteenth century, the remontoir d´égalité made a comeback. It was used in
tower clocks to counter the effects of strong wind on the large exterior hands from finding its way to the gear train and escapement.
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Of
course, the modern wristwatch has very efficient gear-tooth profiles, extremely tight manufacturing tolerances and no need for counteracting the effects of wind
on the hands. What it does have, however, is a tightly coiled main spring. Unlike the constant weight of a clock, the power that the mainspring provides to the
escapement can vary quite considerably from a state of full wind to near empty. In a conventional watch, the amplitude of the balance can vary by up to 60 degrees,
thereby causing an unstable rate.
Instead
of the mainspring powering the balance directly, the mainspring charges the remontoir, which in turn provides a constant force to the balance.
F. P. Journe´s
version of the remontoir d´égalité consists of a small blade spring between the going-train and the tourbillon.
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Tourbillon during assembly
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MAY 2005
INTERNATIONAL WATCH
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