Abstract: An electronic encoder is driven by the cross shaft in the grinder that moves the grinder. The encoder includes a rotary disc constantly driven by the cross shaft, forwardly and rearwardly. Associated with the encoder is an electronic counter in which counting functions are performed in response to the rotation of the disc. An electrical circuit incorporates the encoder and counter, and the electronic circuits of the latter, and includes terminals in common with the encoder and counter. Control signals are entered so that functions are performed according to the position of the grinding wheel, and to move the grinding wheel. The encoder is mechanically connected with the cross shaft in an add-on arrangement. A hydraulic motor drives the cross shaft through a motion transmitting component that includes a hydraulic unit and a mechanical unit in tandem. The entire apparatus is retrofitted, and has mechanical driving connection with the grinder only through the cross shaft.