60E15, 93E03, 26D15.

The paper briefly reviews the concept of the variogram and the estimation error variance in connection with certain estimation problems. This is done in the context of their development in mineralogy. The results are then placed in the context of the assessment of flowing product streams that are continuous space, continuous time stochastic processes. The work in this area, to date, is then briefly reviewed and extended. The paper addresses both practical and theoretical issues, the latter being focused on bounding both the estimation error and the estimation error variance. For this, use is made of variations of Ostrowski's inequality and Holder-type variograms.;