Efficient comminution is core to the economic success of modern gold mining operations. At Newmont Tanami, ongoing efforts to optimise grinding circuit performance have considered evaluation and demonstration of robust efficiency methods to define performance efficiency. This evaluation uses data from a series of plant surveys performed at the Tanami operation, where both single stage ball milling and series ball milling have been used in recent history to process underground gold ore. Circuit efficiency analysis performed using this survey data evaluates the alignment between measured feed ore properties and circuit operating performance against the grinding energy requirements as predicted by conventional desktop methods. This submission therefore provides a foundation for further discussion on best practices in grinding circuit evaluation, including insights into the challenge of predicting ball mill performance in series milling configuration. The inputs and results of the analysis will be provided in full detail specifically to allow industry professionals to follow the workings and reproduce the conclusions, thereby ensuring the paper will become a valuable reference for future studies.