Presently, we are able to measure in situ X-ray diffraction and spectroscopic ellipsometry simultaneously on rotating samples during the deposition process in our AIXTRON 200 RF-S reactor using a commercial available PANalytical Cu ceramic tube as X-ray source. Due to the natural wobbling of the rotating sample, a compensation algorithm is used before adding up single spectra in order to improve signal-to-noise ratio before fitting procedure. The so far used algorithm is based on the detection of peak maxima representing the center of the peak. In this paper we present an improved compensation algorithm based on a symmetric peak shape enabling the calculation of the peak symmetry axes from the center of weight. It is shown that the algorithm improves the resulting peak shapes and is more efficient especially at low diffraction intensities, yielding a higher thickness resolution. (c) 2006 Elsevier B.V. All rights reserved.