A 1D Position Sensitive Detector is well-suited to the test of the short period X-ray multilayer produced for X-ray fluorescence analysis systems and for synchrotron beam lines optics. Because it gives directly the incident and reflected angular beam distributions the PSD avoids the time-consuming scanning mode necessary for the classical detectors. In such tests classical X-ray tubes have been used. Some examples of reflectivity tests for multilayer mirrors with periods ranging from 113Å to 24Å are presented. A way is indicated to improve the 0.03° angular resolution which presently limits our reflectivity measurements possibility.