Abstract: A machine management system, including one or more sensors arranged to take readings of one or more operating variables for a machine. Data processing equipment is arranged to receive data indicative of said operating variable readings for the machine and to analyse the received operational data to determine a probability distribution there-for. The processing equipment includes one or more modules of machine-readable code for assigning a value to one or more Stable distribution parameters in dependence on the received operational data, and a departure in the machine operation from a predetermined normal operating condition is determined from the assigned distribution parameter.