Usability metrics:

• Success rate of tasks (number of errors-typo of errors)

• Completion time (simulation and time on task)

• Completion rate (completed/not completed)

• Knowledge retention (repeat the execution and compare results)

• Next step? Confidence in action (5likert - rating scale for operative performance https://bjssjournals.onlinelibrary.wiley.com/doi/full/10.1002/bjs.4407)

Ergonomics of human-system interaction — Part 11: Usability: Definitions and concepts

The objective of designing and evaluating systems, products and services for usability is to enable users to achieve goals effectively, efficiently and with satisfaction, taking account of the context of use.