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Tachymeter
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A scale on the dial, flange, or bezel of a chronograph that, in conjunction with
the second hand, gives the speed of a moving object. A tachymeter takes a value
determined in less than a minute and converts it into miles or kilometers per hour.
For example, a wearer could measure the time it takes a car to pass between two
mile markers on the highway. When the car passes the second marker, the second hand
will be pointing to the car's speed in miles per hour on the tachymetric scale.
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Tourbillon
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A technically demanding device invented by
Abraham-Louis
Breguet in 1801 to compensate for the interference of gravity on the balance
of a pocket watch, thus improving its rate. In a tourbillon (from the French word
for whirlwind), the entire escapement is mounted on an epicyclic train in a «cage»
and rotated completely on its axis over regular periods of time, usually once a
minute. Though as good as moot in a wristwatch, this superb horological highlight
is seen as a sign of technological
know-how
in the modern era. Due to the current trend toward this complication in haute horlogerie,
watchmakers are now introducing creative variations on the theme such as the Gyrotourbillon I
by
Jaeger-LeCoultre
pictured here.
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Vibration frequency (vph)
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The ring-shaped balance swings around its own axis and acts as the ruling organ
of the movement's escapement. Its amplitude (normally about 300 degrees) is
restricted by the very thin balance spring, which also provides for the reversing
of its direction of rotation. The frequency of the alternating vibrations is measured
in Hertz (Hz)
or in the more usual vibrations
per
hour (vph),
which is also sometimes written
as
a/h,
the a standing for the French alternance (change). Most of today's wristwatches
tick at frequencies of
28,800
vph
(4 Hz)
or
21,600 vph
(3
Hz).
Less usual, but still found in certain models, are vibration frequencies of
18,000 vph
(2.5
Hz)
and
36,000 vph
(5 Hz).
Zenith's El Primero,
introduced in 1969, was the first serial movement to beat at a frequency of
36,000
vph,
and it still does to
this day.
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Water resistance
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Water resistance is an important feature of any timepiece and is usually measured
in increments of one atmosphere (atm or bar, equal to 10 meters of water pressure)
or meters and is often noted on the dial or case back. Watches resistant to 100 meters
are best for swimming and snorkeling. Timepieces resistant to 200 meters are
good for scuba diving.
To deep-sea
dive there are various professional timepieces available for use in depths of 200 meters
and more.
The Hydromax by Bell & Ross (shown) is waterresistant to a record 11,100 meters.
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Courtesy of Wristwatch Annual 2006
© Abbeville Press
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