Functionality refers to the concept of ‘user intuitive.' Based on the writings of Nielsen and other experts who write, the following are standards of functionality: 

• Standardization of functions: all functions listed in same order, in same position
• through application
• Consistency in order of basic functions/tasks
• Consistent error handling and easy reversal of actions
• Consistency of prompts, error messages
• Comprehensible error messages
• Avoid multiple screens, multiple overlapping of screens
• Universal DOS function F1 for Help
• Response time for a user to receive a ‘physical sign' of the result of an action not to surpass 1.0 second in duration
• Quick Loading (or indication of loading times)