question about audio gain

Hello,

In a video I normalize the audio gain like this (-6 db) :

Then for the same video I open again the audio gain window, and I see that the normalize does not displays -6 db but 0 db. Why ?

It is like if it does not remember my setting for normalize for this video. The problem is that I need to know what setting I have chosen for this video (I need to know my last setting (-6 db).).