Abstract: A method for calibrating an apparatus for ellipsometric measurements performed on an arbitrarily large or continuously moving sample, using a visible sample reference frame, and one or more laser sources in order to calibrate the ellipsometer for variations in the distance between the ellipsometer apparatus and the sample of interest. Included are techniques for projecting a first laser beam spot from an incident laser source onto a sample, then analyzing the position of the first laser beam spot relative to the center of the sample reference frame using human-aided measurements and confirmations and/or computer vision techniques. Then adjusting pivot points and/or apparatus-to-sample distance to achieve a first beam spot being located about the center of the sample reference frame, and concurrently intersecting the plane of the sample. Other techniques include changing the incidence and reflectance angle using a semi-circular track arc design with a stepping motor activating each goniometer arm.