Aris, You have to set STEPOVER (Default value: -1); setting SCALLOP HEIGHT is an option. When both are set, the simple answer to your question is that, at any particular place in the tool path calculation, whichever setting gives you the better surface finish (smaller actual stepover) takes charge in the calculation, if necessary. For example, if you are using a Radius Mill (as opposed to a Ball Mill), any flat horizontal surface will probably be machined at the STEPOVER setting (Scallop Height = 0), whereas contoured surfaces will be governed by Scallop Height and the Corner Radius of the End Mill. David