The traditional method of single-angle ellipsometric inversion to determine the refractive index and thickness of transparent films is re-examined. Error formulas are derived and analyzed. It is shown that consideration of these errors allows the improvement of the determination of thickness and then that extraction of refractive index can be performed with improved confidence by an additional calculation step. The method is tested through different sample examples. It should be helpful in many practical cases of ellipsometry data interpretation, especially when standard fitting techniques do not work. (C) 2013 Elsevier B.V. All rights reserved.