Sanditthika Sutta: Visible Here-&-Now In the Sanditthika Sutta,


  "The fact that when a delusive quality is present within you, you discern that a delusive quality is present within you; and when a delusive quality is not present within you, you discern that a delusive quality is not present within you"


A similar description is also given in the Satipatthana Sutta. The second part, "to know when something is not present inside of me", is to be understood how? Do I literally acknowledge at any point in my daily life that I have currently no defilements in me? And if the answer is yes, what do I do with that acknowledging?
The four right efforts in the noble path are: 


effort to prevent unwholesome mental states.
effort to abandon unwholesome mental states.
effort to develop wholesome mental states
effort to maintain &amp; increase wholesome mental states


Therefore, when the mind without delusion is discerned, the effort is made to maintain the mind without delusion, which requires governance or supervision by mindfulness.