1. In a photo lithography process on a photo resist coated substrate, a method for determining the effect of flare on line shortening, the method comprising: in a first exposure at a first die position on the substrate, printing on the substrate a dark-field mask including a first portion of a flare pattern corresponding to a corner of the dark-field mask, a first portion of a box-in-a-box correction pattern, and a first portion of a focus box pattern, and in a second exposure at the first die position, printing on the substrate a clear-field mask including a second portion of the flare pattern corresponding to a corner of the clear-field mask, a second portion of the box-in-a-box correction pattern, and a second portion of the focus box pattern; at a second die position on the substrate, printing on the substrate a composite mask pattern based on features of the dark-field mask and the clear-field mask; developing the printed patterns and obtaining measurements therefrom; and determining the effect of flare as a function of the measurements.