Some aspects of the present disclosure provide for a method of accurately simulating variations in an operating parameter, due to processing variations caused by a multi-patterning exposure, by reducing the impact of layout sections having a large width and spacing. The method assigns a skew sensitive index to one or more sections of a multi-patterning layer formed with a first mask. Runlengths of the one or more sections are respectively multiplied by an assigned skew sensitive index to determine a skew variation for each of the one or more sections. The overall skew variation sum is then determined by summing the skew variation for each of the one or more sections. By separately determining the effects of processing variations (e.g., mask misalignment) for different sections of a multi-patterning layer, an accurate measurement of operating parameter variations is achieved.