A method, system and computer program product for determining an Azimuth angle of an incident beam to a wafer are disclosed. A method comprises: using the incident beam to make a first set of measurements of calibration targets of a first set of grating angles that are different than one another; analyzing the first set of measurements to determine an reference grating angle which corresponds to a grating line to which the incident beam has a practically zero Azimuth angle; and determining the Azimuth angle of the incident beam to the wafer using the determined reference grating angle.