Any measurement resolution is limited by random fluctuations, "noise", of the measured quantities. Practical systems also might experience variations of parameters causing "drifts" in the measurements. Various sources of such noises and drifts may take different time or frequency dependencies. To understand how such fluctuations affect one's measurement, a careful analysis of such noise and drifts must be performed. Discrimination of such noise sources might be performed by performing Allan deviation measurement of discretely sample data. In this blog post, we discuss how to easily measure Allan variance with our Zurich Instruments lock-in amplifier.