Glossary  A - B   C - F   G - L   M - P   Q - S   T – W

Tachymeter   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.     Tourbillon   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.     Vibration frequency  (vph)   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.     Water resistance   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.

Courtesy of Wristwatch Annual 2006 © Abbeville Press  A - B   C - F   G - L   M - P   Q - S   T – W