I'm trying to use a dialog scroll item as a volume control, and I know that there's a scroll event, but I'm unable to determine any difference between clicking the left hand arrow, the right hand arrow or along the length of the dialog item.

The format that I'm using for that dialog item is

There is no difference, it's all moving the scrollbar thumb. All you have to do is wait for a scrollbar event, and then set the new volume to $did().sel