An X-ray diffractometer having a simple yet accurate means for locating the surface of the sample to be examined with respect to the zero point of the X-ray (RS) is disclosed. Briefly stated, a laser (LA) and camera (KA) are positioned at preferably 90.degree. with respect to each other such that the intersection of the optical axis of the camera and the laser passes through the zero point of the diffractometer. In this fashion, the camera will see at its center, the zero point of the X-ray despite the fact that the X-ray is of course invisible to the naked eye. Accordingly, by movement of the sample (P) with respect to this camera image, the true and correct zero point of the X-ray with respect to the surface of the sample to be examined may be determined without the need for experimental and unnecessary X-ray or examination runs being taken.