Quantitative Usability Metrics: Task Success, Time, and SUS

Usability is not purely qualitative; it is measured with rigorous mathematical metrics:

1. Task Completion Rate (Binary 0 or 1): The percentage of participants who successfully achieve the task goal without facilitator intervention (benchmark: > 78%).
2. Time on Task (Seconds): The duration required to complete the task.
3. Error Frequency: Count of mis-clicks, wrong turns, and error messages triggered.
4. System Usability Scale (SUS): A validated 10-item questionnaire yielding a score from 0 to 100. A score of 68 is the global average; 80+ indicates world-class usability.