For a secure encryption of original data the original data are first of all encrypted using an encryption key or an encryption algorithm. Only an in-phase or quadrature component of the training signal generated in the demodulation circuit is used for equalization convergence. Using the conversion table, the image data D is converted into the image data D\u2032 to generate a proof with the area percentage of black being saved. A Hyfax may secure to the slide rail interposed between the track and slide rail to reduce friction therebetween.