This way also uses two experimental protocols,  and , to compare the index effect  with the effect  of moderation alone. The index protocol  is executed first; the response of prime interest,  is observed, and the response  of the moderating variable is also measured. With that knowledge, then the fixed driver, moderation imposed protocol  enforces that  with the driving variable  held fixed; the protocol also, through an adjustment  imposes a change  (learnt from the just previous measurement) in the moderating variable, and measures the change  Provided that the moderated response is indeed that  then the principle states that the signs of  and  are opposite.
Again, in other words, change in the moderating state variable  opposes the effect of the driving change in  on the responding conjugate variable