Precision oscillators are ubiquitous in modern electronic systems, and their accuracy often limits the performance of such systems. Hence, a deep understanding of how oscillator performance is quantified, simulated, and measured, and how it affects the system performance is essential for designers. Unfortunately, the necessary information is spread thinly across the published literature and textbooks with widely varying notations and some critical disconnects. This paper addresses this problem by presenting a comprehensive one-stop explanation of how oscillator error is quantified, simulated, and measured in practice, and the effects of oscillator error in typical oscillator applications.