This paper discusses a case study application of inferential measurement models for semiautogenous grinding (SAG) mills and is the fourth paper in a series of five papers on inferential measurement of SAG mill parameters. The development of the inferential measurement models of SAG mill discharge and feed streams and mill rock and ball charge levels, detailed earlier in the series, is summarised here. The models are then tested on plant data for validation and analysis. Model characteristics are explored to highlight model sensitivity and relative uncertainty. The results are encouraging while limitations are noted and potential avenues for further research are discussed. (C) 2009 Elsevier Ltd. All rights reserved.