ABSTRACT
Before introducing the various components of the Overall Estimation Error OEE, it is beneficial to proceed with an introduction to the fundamental notion of heterogeneity. To find out how it is defined, and to clearly differentiate this notion from the notion of homogeneity. It does not involve a great deal of research to find out that homogeneity is often a relative concept. If we look at a pile of fine sand from a distance, the pile may appear homogeneous; however, we know that as we come closer toward the pile and finally look at it under a magnifying glass, we realize that the homogeneity was only an illusion.
