A process (300) is disclosed to measure predetermined wavelength reflectance spectra of a photo resist coated wafer (305,310,315,320) at a nominal thickness. After coating, the predetermined wavelength reflectance (325,330) is measured and the peak heights and valleys in the vicinity of the predetermined wavelength are tabulated. The relative swing ratio is computed (335) as the average peak height of the spectra at the exposure wavelength. This relative swing ratio is then compared to similar computations on other processes to determine which provides the best critical dimension (CD) control.