Hi,

The Blink tool has a series analysis routine that provides the functionality that you want. For image grading, the

SubframeSelector script is the most comprehensive and versatile tool available.

On a side note, you have much better estimators than the mean and the standard deviation in PixInsight. For location (central value) and scale (variability) we provide a number of robust estimators that give much more accurate and useful information on images. For example, Blink's series analysis provides median and median absolute deviation (MAD) estimates.