A constraint is inserted into a program to address a vulnerability of the program to attacks. In the head forming process, a planned area is secured on a light source placing surface of a slider substrate, then a magnetic head part is formed on a head area other than the planned area and a spacer for securing a mounting space for the laser diode is formed on the planned area. An attached handle would facilitate its withdrawal onto a platform during examination and for subsequent re-insertion into the metal container. A PN code replica prepared by the receiver terminal operates on the second input signals to detect the polarity of the navigation bits and correct the polarity of the bits so that the bit polarity of the second input signals are always positive. An alternate alert system includes a receiver unit coupled with a computer that allows either the user or a vendor computer to monitor the status of the sensor and respond accordingly. The proportion of the text \u201cread\u201d by each participant and the pace at which the lesson progresses can each be automatically altered based upon the proficiency of the student.