How to numerically edit key frame volume in track envelope?

How does one numerically edit key frame volume in track envelope? If I want to change the key frames in the track envelope, I can't seem to edit them manually.  If I move to a previous key frame, and then manually change the little blue volume number next to the volume circle, the key frame volume doesn't change. Why? I'd like to be able to edit the key frames numerically instead of changing them manually so that they are exact. Any suggestions? I'm new to Audition.