y a crystal depends on the shape or physical properties (sometimes referred to as the cut) of the crystal. On the other hand, the stability of the output signal is also heavily influenced by many environ- mental factors, such as temperature, humidity, pressure, vibration, and magnetic and electric fields. Engineers refer to this as the sensitivity of the oscillator to environmental factors. For a given oscil- lator, the sensitivity to one factor is often dependent on the sensitivity to another factor, as well as the age of the crystal or device itself. As a real-life example, if your wristwatch is using a 32,768-Hz quartz crystal oscillator, the accur- acy of the wristwatch in different environmental conditions will vary. The same behavior also ap- plies to other electronic equipment, including transport devices and routers in the network infra- structure. This means that when electronic devices are used to synchronize devices to a common frequency, phase, or time, the environmental conditions adversely impact the stability of synchronization. The accuracy for wristwatches is usually measured in seconds or minutes, while for other tasks involving net- work transport, the accuracy requirement is frequently small fractions of a second-microseconds (millionths of a second) or even nanoseconds (billionths of a second). There have been many innovations to improve the stability of crystal oscillators deployed in un- stable environmental conditions. One common approach in modern designs is for the hardware de- signer to design a circuit to vary the voltage being applied to the oscillator to adjust its frequency in small amounts. This class of crystal oscillator is known as voltage-controlled crystal oscillators (VCXO). Of the many environmental factors that affect the stability and accuracy of a crystal oscillator, the major one is temperature. To provide better oscillator stability of crystal against temperature vari- ations, two additional types of oscillators have emerged in the market: Temperature-compensated crysta