RF engineers would love to get their hands on an ideal crystal oscillator circuit. That is, a quartz crystal oscillator that transmits at the designated frequency for the entire life of the device without any frequency deviation. Unfortunately, that ideal circuit world is a mathematical fantasy.
There are many factors that contribute to quartz oscillator stability and frequency drift issues. To prevent these problems as much as possible, it's important to have a firm understanding of precise frequency stability. This will give you the tools to keep your applications performing optimally. But there's another problem...