caption: 12 Usability Metrics time to complete a task time spent in error time spent using help or documentation ratio of success and failure number of commands used number of times the user is misled by the interface number of times the user expresses frustration or satisfaction number of good or bad features recalled by the user time to reach a specific level of performance frequency and type of errors made by users user reaction times to particular tasks frequency of command usage, e.g.
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