One or more non-zero diffraction orders are selected, and these selected one or more zero or non-zero diffraction orders are selected for eliminating or obtaining corresponding zero or non-zero diffraction order terms or interference term from measurements from a periodic target using an optical metrology tool. The periodic target has a pitch, and the measurements contain a zero diffraction order and one or more non-zero diffraction order terms. Using the optical metrology tool, an incident beam is directed to positions on the target, and the measurements are obtained from the target in response to the incident beam. The measurements are processed to eliminate or obtain each zero or non-zero diffraction order term or interference term associated with each selected zero or non-zero diffraction order, resulting in a processed metrology signal. The positions are shifted from each other so as to cause the zero or non-zero diffraction order term or interference term corresponding to each selected zero or non-zero diffraction order to be eliminated or obtained.