Monitoring during emergencies in dynamic environments is widely recognized to be an active, selective attention, process. In contrast monitoring during normal operations is often thought to more closely resemble a vigilance task. This paper describes a field study of power plant operator monitor during normal operations. We observed and interviewed 27 operators at two different plants for a total of over 200 hours. Despite differences in control room technology, we found that in both cases operators devised active strategies to remove or reduce meaningless changes from the interface, create information different from that intended by the designers, and make important information more salient. These findings were integrated into a model of operator monitoring, that emphasizes operators' use of strategies for knowledge-driven monitoring and proactive adaptation of the control room interface. The model is equally applicable for normal and emergency operations and underscores the commonality in cognitive demands in both environments.