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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.
The ring-shaped balance swings around its own axis and acts as the ruling organ of the movement's escapement. The amplitude (normally about 300 degrees) is restricted by the very thin balance spring, which also provides for the reversing of the 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). |
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