No / The analysts need timely and accurate information to conduct proactive action over complex situations. Typically, there are thousands of reported activities in real time operation, although, to direct the analysts attentions to the most important one, researchers have designed multiple levels of situational awareness (SWA). Each process lends itself to ranking the most important activities into a predetermined order. According to our best knowledge, less attention has been given to the performance evaluation with regards to the prioritisation stage. Specifically, the performance metric, "The Activity of Interest Scores" has not considered corner cases of different situational assessments needs and configurations. Originally, it had not been designed for measuring the capability of the SWA system. In this paper, we have proposed a new performance metric, as well as a guidance case study for measuring the ranking capability of SWA systems. Our initial result shows that, The Ranking Capability Score has provided an appropriate scoring scheme for different ranking capabilities of SWA systems.