The difference between Volume and Volume Trim in Protools

[Ailin Gong]

Hi guys,
As title, I am not sure the difference between Volume and Volume Trim in the dropdown automation window on the tracks in protools. As I tried that I found when I am in Touch mode and use the volume trim, it would automate on my exist volume automation line. ( Actually when I am in volume trim mode, I can't see the automation changes, that confuses me either. But when I go to the volume mode, I find it re-write my volume line. )
Can anyone explain that to me please?
Thank you very much.

[albee1952]

Youtube has some videos to explain this better, but it appears(to me) to simply be a way of resetting track faders(not track volume, just fader position) so that you can do automation rides(riding the fader to write automation) with the fader starting at -0, around which, the fader has the most resolution(so you get the smoothest writing of new automation). When you exit TRIM mode(assuming you made fader moves), the fader will snap back to its true volume setting. Watching some videos will help this make more sense(and if someone thinks I have done a poor job explaining, please correct me)

[Ailin Gong]

I will try to look up some videos. Thank you very much!