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The Indicator Lights Interface 33 These nine indicators appear in a small window that measures about 1 x 2 on the user s display These indicators require a modest amount of screen real estate a resource that is precious to users during normal operation Because the expected benefit of the indicators outweighs its cost in screen real estate I expect the user will keep this indicator window visible at all times Note however that while the user investigates a problem indicated by the interface the screen real estate requirements increase This change in resource consumption is appropriate during periods when the user is actively engaged with the interface 8 Each indicator light can signal one of four states about the subsystem it monitors x Operating normally x Developing a problem or experiencing a noncritical problem x Experiencing a critical problem x Indicator not operational or status unknown The first three of these states are color coded to one of three urgency levels normal warning and critical By default the colors associated with these urgency levels are green yellow and red I chose this color scheme to make it easy for users to remember since green yellow and red correspond to the colors used to signify similar meanings in many situations in the United States most notably traffic signs and signals This color scheme is not without its own difficulties For instance some users may be using a monochrome monitor others may be color blind and not all cultures use green yellow and red for these meanings For these reasons the user can easily customize the color scheme used to represent these three urgency levels In fact the user can forego the use of color and instead use different grayscale levels to signify the different urgency levels Figure 4 1 shows two views of the indicator window one in the default green yellow red color scheme and one in a monochrome scheme 8 a Color Scheme b Monochrome Scheme Figure 4 1 Indicator Lights This figure shows two views of the

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