Abstract: An arrangement for inspecting the surface of a rotating object (1) which includes object retaining means for retaining whilst rotating the object, means (3) for irradiating the surface of an object when retained and rotated by the object retaining means with a first beam of optical radiation, means (5) for irradiating the surface of an object when retained and rotated by the object retaining means with a second beam of optical radiation detectable as distinct from the first beam, detector means (7) for detecting radiation reflected by the surface of the object from the first beam and for detecting radiation reflected by the surface of the object from the second beam and a signal processor (15) for receiving signals produced by the detector means and for analysing such signals wherein the first beam and the second beam are of different wavelengths or in different wavelength bands and the detector means is capable of simultaneously receiving and detecting radiation received from the same irradiated area of the