Ball milling circuit operation is complex due to the interactions between the circuit components; as such, there is little to be gained from attempting to optimise the milling or classification stages independently. Circuit optimisation is best undertaken with a holistic approach, and a well-proven system is the Functional Performance Evaluation as developed by Metcom Technologies, a framework for differentiating efficiencies that are blended in every operating ball milling circuit. This framework offers metallurgists and operators a more insightful understanding of the mechanisms at work inside a ball mill grinding circuit and allows rapid identification of the causes of poor grinding performance. This analysis involves assessing mill power draw along with grinding and classification efficiencies, including a full review of all mineral characteristics test work and circuit operating data. ME Elecmetal has used this framework to assist customers with grinding circuit optimisation, and this paper presents three case studies where the method has been employed.