Range – Here you can choose Shadows, Midtones, or Highlights. Dodging and burning will emphasize these tones.
Exposure – Here you can determine the strength of the dodge/burn tools. Default is 50%.
You can retrace to build up dodge/burn effects in a painterly fashion. The default exposure of 50% works well in this regard. Excessive dodging or burning can be undone with Ctrl-Z (undo) or backing up to a previous version in the History palette.
The Dodge and Burn tools change image pixels. This makes it difficult to undo or make changes at a later date. Although you can control range and exposure, the controls are somewhat primitive. You cannot, for example, increase or decrease contrast.