2. Visibility of System State:
Software typically has state (to state the obvious), such as “where” you are in the software’s menu system, what “mode” you are currently in. whether your work is safely stored on disk or has “unsaved changes”, what stage of a process you are up to and how many steps are left. Failure to effectively communicate system state to the user is inviting them to get lost and make mistakes. counterexamples: setting the time on a digital wrist watch, programming a VCR
3. Discoverability
this is about making the possible actions in a system visible- or if not immediately visible, the mechanism of their discovery should be visible and consistent. For instance, the menu items in a GUI system are discoverable. the available commands in a unix system are not. the opposite of this principle is “hidden interface”, examples of hidden interface are rife in iOS: tapping the top of the screen for “scroll to top”, shake to undo, swipe from edge for browser back- etc.