It also works if the button is not labeled, as long as the state is clearly visible in the environment and the link is clear. Consider the light switch - if th

It also works if the button is not labeled, as long as the state is clearly visible in the environment and the link is clear. Consider the light switch - if there’s just one, it’s the best UI ever. You know what to do to turn the lights off, just flip the closest switch. Obviously if there’s more than one then it’s the worst UI ever. Another example, a smartphone’s side button (screen on/off).