Quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks. Generally, some form of digital logic counts the cycles of this signal and provides a numeric time display, usually in units of hours, minutes, and seconds.Since the 1970s, they have become the most widely used timekeeping technology. Chemically, quartz is a compound called silicon dioxide. When a crystal of quartz is properly cut and mounted, it can be made to vibrate, or oscillate, using a constant electric current. If the crystal is accurately shaped and positioned, it will oscillate at 32,768 Hz, and once the circuit supplying power to the crystal counts that this number of oscillations have occurred, it increases the recorded time by one second. This property, of changing shape under an electric current, is known as piezoelectricity.
Such crystals were once used in low-end phonograph cartridges: the movement of the stylus (needle) would flex a quartz crystal, which would produce a small voltage, which was amplified and played through speakers. Many materials can be formed into plates that will resonate. However, since quartz can be directly driven by an electric signal, no additional speaker or microphone is required. Quartz has the further advantage that its size does not change much as temperature fluctuates. Fused quartz is often used for laboratory equipment that must not change shape along with the temperature, because a quartz plate's resonance frequency, based on its size, will not significantly rise or fall. Similarly, a quartz clock will remain relatively accurate as the temperature changes. he relative stability of the resonator and its driving circuit is much better than its absolute accuracy.
Standard-quality resonators of this type are warranted to have a long-term accuracy of about 6 parts per million at 31 °C: that is, a typical quartz wristwatch will gain or lose less than a half second per day at body temperature. If a quartz wristwatch is "rated" by measuring it against an atomic clock's time broadcast, and the wristwatch is worn on one's body to keep its temperature constant, then the corrected time will easily be accurate within 10 seconds per year.
This is more than adequate to perform celestial navigation. Some premium clock designs self-rate. That is, rather than just counting vibrations, their computer program takes the simple count, and scales it using a ratio calculated between an epoch set at the factory, and the most recent time the clock was set. These clocks usually have special instructions for changing the battery (the counter must not be permitted to stop), and become more accurate as they grow older. It is possible for a computerized clock to measure its temperature, and adjust for that as well. Both analog and digital temperature compensation have been used in high-end quartz watches.
