A computer derives, from a current measurement of an attribute of a system, an instantaneous severity score based on a probability model that is determined from prior measurements. The computer then displays, for several successive moments in time, either the instantaneous severity score or an aggregated severity score obtained from a set of instantaneous severity scores (e.g. by averaging). Each set of scores to be aggregated may be identified by, e.g., a fixed-width time window located at a fixed offset from a moment in time at which the aggregated score is to be displayed. Aggregation suppresses or dampens momentary abnormalities, which would otherwise get displayed. In some embodiments, graphs for multiple categories of metrics are displayed on a single screen, aligned in time, to enable a human operator to form a visual correlation therebetween, e.g. to identify causes of atypical performance in the system.