An analysis system that includes a processor and an memory module; wherein the memory module is arranged to store aerial images of an area of a mask, each aerial image corresponds to focus value out of a set of different focus values; wherein the processor is arranged to find weak points by processing the aerial images using different printability thresholds; and wherein the processor is arranged to determine focus and exposure values for generating a Process Window Qualification (PWQ) wafer to be manufactured using the mask in response to focus and exposure values associated with the weak points.