A saw blade for a machine tool driven oscillatingly about a longitudinal axis has at least one cutting edge, on which, at least in part, abrasive particles are provided. A bottom rail 111 attached to the bottom end of the shade incorporates spring-biased brake assemblies engaged in longitudinal slots 115A, 115B of side rails 117A, 117B. A surface of the first optical waveguide includes a diffraction grating capable of introducing-extracting-sending back light into and from the first optical waveguide. Biometrical data for files where the temporal period of the limitation has passed are ignored to reduce the number of files with which the comparison must be made reducing the number of false matches.