Standardized performance trajectory as a measure of usability

Color specification is a time consuming and challenging task in computer graphics applications. In order to investigate how certain fundamental attributes of any color selection system may affect its usability, we systematically varied both color space and navigational device and measured simultaneously several usability parameters during a simple color matching task. A new analysis method called the Standardized Performance Trajectory (SPT), was used to measure the rate of convergence during color specification as an indication of a system's ease of understanding. The SPT analysis revealed significant results that the traditional usability measures did not. The purpose of the paper is to describe the SPT and to discuss its merits.