A method and system are presented for use in measuring/inspecting a patterned article. Optical measurements are applied to a measurement site on the article by illuminating the measurement site with a plurality of wavelengths at substantially normal incidence of the illuminating light, detecting light returned from the illuminated site, and generating measured data indicative thereof. The measurements are applied to the measurement site through a polarizer rotatable between its different orientations selected from a number of pre-calibrated orientations.