1. A system controller comprising: a receiver for receiving data about a system to be controlled and for associating the received data with a time factor; a summariser for updating a set of summary bins, each of which covers a respective period of time, and each of which stores a summary of the received data having a time factor which falls within the respective period of time covered by the summary bin; a processor for processing the summary bins; and a director for issuing control instructions to the system to be controlled based on the results of the processor; wherein the periods of time covered by respective summary bins include overlapping periods of time and periods of time having different durations.