learnability | how fast a new user can learn the system | having fewer things to learn, or by making the learning process more intuitive | a user might be able to learn the most important 20% of the system in 3 days if the system is simple and intuitive; 7 days if the system is simple but non-intuitive, and 11 days if the system is complex and non-intuitive | ordinary use | The speed with which a new user can become proficient with the system | hard to assess | 7.4 - The Basics of User Interface Design | learning curves | software quality | information overload |