They are widely used in many electronic devices ranging from simplest clock generators to digital instruments (like calculators) and complex computers and peripherals etc. Almost any object made of an elastic material could be used like a crystal, with appropriate transducers, since all objects have natural resonant frequencies of vibration. Natural quartz is much more sensitive than artificially grown crystals, and sensitivity can be further reduced by sweeping the crystal – heating the crystal to at least 400 °C in a hydrogen-free atmosphere in an electric field of at least 500 V/cm for at least 12 hours. The above figure is a 20psc New 16MHz Quartz Crystal Oscillator and it is one kind of crystal oscillators, that works with 16MHz frequency. The annealing is faster at higher temperatures. The orientation of the cut influences the crystal's aging characteristics, frequency stability, thermal characteristics, and other parameters. The short-term stability is measured by four main parameters: Allan variance (the most common one specified in oscillator data sheets), phase noise, spectral density of phase deviations, and spectral density of fractional frequency deviations. A double rotated cut ("Linear Coefficient") with a linear temperature-frequency response; can be used as a sensor in crystal thermometers. High magnitudes of shocks may tear the crystals off their mountings (especially in the case of large low-frequency crystals suspended on thin wires), or cause cracking of the crystal. BVA??  Neutrons also alter the temperature-frequency characteristics. Generally the ring has an odd number of inverting stages, so that there is no single stable state for the internal ring voltages. Silver can be passivated by exposition to iodine vapors, forming a layer of silver iodide. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators, and oscilloscopes. E.g.  The level and character of impurities can be measured by infrared spectroscopy. Any small additional capacitance in parallel with the crystal pulls the frequency lower. Oscillators are often characterized by the frequency of their output signal: Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters. But, like many other mechanical resonators, crystals exhibit several modes of oscillation, usually at approximately odd integer multiples of the fundamental frequency. Operates in thickness shear mode. Cady, and as a 50 kHz oscillator in the first crystal clock by Horton and Marrison in 1927. The first of these was the Barkhausen–Kurz oscillator (1920), the first tube to produce power in the UHF range. The wave shape and amplitude are determined by the design of the oscillator circuit and choice of component values.