I added one more - Expose state of the system to user. Examples include: - Vintage radios with sliding marker that shows what the current station freq is - 3 s

I added one more - Expose state of the system to user. Examples include: - Vintage radios with sliding marker that shows what the current station freq is - 3 state sliders that show whether something is state A/B/C by simply looking at it. When performing action on such a slider, user immediately knows by the means of performing the action, what the state of the system is! - Volume knobs, shows the current state. - Big bright ON light when a Keithley power supply is supplying power - Lots of Braun products, too many to list. May be these are obvious but it just reminds me that things we take granted are really important in UX/UI.