When Parameter Spacer number is at zero, the actual spacer dimension is approximately 100 um.  I set most of my crown spacer between -40 to -20 and inlays at around -50 (subtracting from 100 um). We are able to obtain an more ideal spacer range with smooth preparation images. Using Ctrl + B in the Milling Preview screen will provide visual verification that the restorations will seat passively. To activate this feature, double click on Trim command in the Milling Preview screen to view virtual die without the blue margin line, rotate die to underside and hit Ctrl + B on the keypad to view spacer.  If a "shine through" is observed, then increase spacer dimension in the Parameter window until no shine through in the spacer is viewed. This spacer check and balance step will assure a restoration seat without internal binding.