During an abnormal event, control room operators must rely on the available information in the human-system interface (HSI) to understand and make sense of what is going on and make the right decisions. Under some conditions the instrumentation may fail and result in missing or incorrect information. Klein's data/frame theory postulates that when making sense of a situation, people start with an initial hypothesis or frame and this frame influences what data they attend to. And conversely, the available data is used to elaborate the frame or to detect inconsistencies in a frame. This paper presents an empirical simulator study of how two crews of nuclear control room operators handled incident scenarios with degraded indications. The data-frame theory is used as a theoretical approach to investigate the control room crew's decision-making when information in the HSI is degraded. More specifically, we examine what strategies the control room crew uses to decide that indications are degraded, under what conditions they fail to notice degraded indications, and how operators' ability to handle an incident is impacted.