Tumbling mills play an essential role in modern mineral processing. Because of the nature of the mill, the internal forces make instrumentation of the mill interior difficult. One solution to this problem is the use of an instrumented ball. An instrumented ball, equipped with an accelerometer, rotation rate sensors and a temperature sensor has been built. The instrumented ball and a camera system are used to measure the state of the charge within a laboratory mill. In parallel, a discrete element model (DEM) of the laboratory mill is developed. Using the distributions and moments of the energy terms of the charge, the simulation and experimental results are analyzed and compared. The moments are used to tune the DEM, such that the simulation results are in agreement with the experimental results. The comparison also identifies which aspects require further improvement. (C) 2012 Elsevier Ltd. All rights reserved.