So far in this module, we have learned that humans vary in sensory, cognitive, and physical abilities and attributes.  We have learned that these variances can be measured and analyzed.  These variances contribute to differences in human task performance.  Performance differences also can be measured and predicted using appropriate statistical techniques.

These measurements and predictions provide a powerful tool in designing and evaluating systems.  For example, to design a new Personal Computer (PC), knowing users' maximum key activation speed in keyboarding will enable us to calculate how fast the computer will have to respond, so that there is no perceived delay.  Slow computer response may annoy the user and may also slow user task performance.

Successfully accommodating variance in human performance is a critical determinant of the "usability" of a system.  Usability criteria need to be determined at the beginning of system design, applied iteratively throughout development, and used to assess the final resulting system.

	En Route Air Traffic Controllers, using the Display System Replacement (DSR).
Human performance abilities must be factored into system design.