Watch glossary: U, V, W, Z.
UNIDIRECTIONAL ROTATING BEZEL
An elapsed time rotating bezel, often found on divers' watches, that moves only in a counterclockwise direction. It is designed to prevent a diver who has unwittingly knocked the bezel off its original position from overestimating his remaining air supply. Because the bezel moves in only one direction, the diver can err only on the side of safety when timing his dive. Many divers' watches are ratcheted, so that they lock into place for greater safety.
UNIVERSAL TIME
The mean solar time of the Greenwich meridian, counted from noon to noon, Often confused with the mean time notion.
VARIATION
In horology the term is usually referred to the variation of the daily rate, i.e. the difference between two daily rates specified by a time interval.
VIBRATION
Movement of a pendulum or other oscillating bodies, limited by two consecutive extreme positions. In an alternate (pendulum or balance) movement, a vibration is a half of an oscillation. The number of hourly vibrations corresponds to the frequency of a watch movement, determined by the mass and diameter of a balance and the elastic force of the balance spring. The number of vibrations per hour (vph) determines the breaking up of time (the "steps of a second hand). For instance, 18,000 vph equals a vibration duration of 1/5 second; in the same way 21,600 vph = 1/6 second; 28,800 vph = 1/8 second; 36,000 vph = 1/10 second. Until the 1950s, wristwatches worked mostly at a frequency of 18,000 vph; later, higher frequencies were adopted to produce a lower percentage of irregularities to the rate. Today, the most common frequency adopted is 28,800 vph, which assures a good precision standard and less lubrication problems than extremely high frequencies, such as 36,000 vph.
WATER RESISTANT or WATERPROOF
A watch whose case is designed in such a way as to resist infiltration by water (3 ATM, or atmospheres, corresponding to a conventional depth of 30 meters; 5 atmospheres, corresponding to a conventional depth of 50 meters.)
WHEEL
Circular element, mostly toothed, combines with an arbor and a pinion to make up a gear. Wheels are normally made of brass, while arbors and pinions are made of steel. The wheels between barrel and escapement make up the so-called train.
WINDING STEM
Element transmitting motion from the crown to the gears governing manual winding and setting.
WINDOW
Aperture in the dial, that allows reading the underlying indication, mainly the date, but also indications concerning a second zone's time or jumping hour.
WORLD TIME
Additional feature of watches provided with a GMT function, displaying the 24 time zones on the dial or bezel, each zone referenced by a city name, providing instantaneous reading of the time of any country.
ZONE
Small additional dial or indicator that may be positioned, or placed off-center on the main dial, used for the display of various functions (e.g. second counters).
ZODIAC
Circular belt with the ecliptic in the middle containing the twelve constellations through which the sun seems to pass in the course of a year.
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