I'm not sure why you think that "usually, stereo is measured between -1 to 1." ProTools measures it from -100 to +100, Samplitude 0 to 2, Reaper -1 to +1 and I could go on but the answer to your question is that Audition uses -1 to +1.
But you see those are track pan values I'm talking about and you are looking at clip pan values which range from 0 to 1 so Audition has two scales, one for track pan and one for clip pan and as such I would think that the values you are looking at should now be pretty obvious.
As to how you 'interpret' them I would suggest that you look at each of the keyframes (from memory if you hover over or click on the keyframe it will reveal it's value and you should then be able to relate those values back to each of the seven values in the sesx
Thank you,
In fact, KeyFrames values are scaled from 0 to 1, that concerns right speaker pan level. For left value : L = 1 - R. 0,5 is the center value (L=R=0.5).When the level is from 0 to 1, it seems that the formula is Linear power panning. When the values are scaled from -1 (or -100) to 1, the formula is Constant power panning.