Audemars Piguet Calibre 2875 Instructions For Use Manual - 2.1 Tourbillon
2.1 Tourbillon
In the second half of the 18th century, the most advanced watchmakers were
working on improving the accuracy of timing. Achieving identical setting of
watches in all the vertical and horizontal positions still remained one of the major
problems. In the vertical positions in particular, terrestrial attraction disturbs the
regulating organ (balance wheel/spring) at the slightest change in equilibrium, thus
causing rate variations in the watch.
In 1801, the watchmaker Abraham-Louis Breguet created a tourbillon system that
would balance rate variations in the various vertical positions.
The operating principle has all in all remained the same to the present day: the
escapement components (wheel, pallet and balance) are not fitted rigidly in the
movement, but are carried by a mobile cage. This cage rotates around its axis
together with the escapement components, at a rate of one revolution per minute,
and by its constant rotational motion compensates for rate variations in the vertical
positions (see figure below).
185 years later, in 1986, Audemars Piguet succeeded for the first time in fitting this
system in a wristwatch with an automatic extra-thin movement. This automatic
movement is provided with the smallest cage ever built, with an outer diameter
measuring only 7.6 mm. With the escapement wheel included, this cage consists of
no less than 60 different parts and weighs only 0.136 gramme.
2.2 The automatic winding system
The first use of an automatic winding mechanism with an oscillating weight
having limited or sector rotation dates back to 1986, in what was then the thinnest
and smallest tourbillon watch in the world. For this model (ref. 25643 /BA/PT,
cal. 2870), revolutionary technological solutions had to be employed. Automatic
winding is driven by a weight in platinum/iridium, one of the heaviest of all metals,
ensuring watch winding in all conditions.