1. Time to complete a task2. Number of user commands to complete task3. Fraction of task completed4. Fraction of task completed in a given time5. Number of errors6. Time spent on errors7. Frequency of online help used8. Number of available commands not used9. When task is repeated, ratio of successes to failures10. Fraction of positive comments made by user11. Fraction of good to bad features recalled by user12. Number of expressions of frustration and satisfaction13. Number of times user loses control over system14. Number of times the user needs to devise a way of working around the problem/system.