The active aspects of crushing must be considered in order for processing plants to achieve their goals and objectives in an efficient and cost effective manner. Active crushing involves the consideration of time-dependent effects. This differs from traditional simulation approaches which consider the whole process to be in a steady state condition. Key aspects of active crushing include crusher process strategies, crusher design strategies and circuit operation/design. These aspects allow the role of the machine to be understood at various levels of deployment and the performance envelopes of the equipment and plant circuit to be marched. For too long active crusher performance has been overlooked, often because the real performance is averaged over time. As such the process efficiency of the machines is generally no better than adequate. Operating crushers in an active role, this level of performance is not acceptable and improvements in this area can only result in the improvement of overall plant performance. To give a guide to the magnitude of time dependent effects a Case Study is reported in this paper. Mathematically modelling the crushing process including time dependencies, allows the effect of time-related variations and thus the whole process to be better understood. If need be, output can be incorporated into crusher design and operating variables to ensure less sensitivity to small changes in feed and other time dependent variables. Improved monitoring to ensure early detection of time dependent changes should also lead to a more efficient and stable process.