These three parameters control how the value you enter in the accompanying box will be used.
Constant
The value you enter will be used.
Cutter Radius
The value you enter will be multiplied by the radius of the tool.
Step Size
The value you enter will be multiplied by the applicable Step Size. This option is available only on Plunge Information and 2 Axis related Lead Information (including Z Rough and Z Finish) dialog boxes.