Resilient attachment members interconnect a pair of flat plates of a movement detector pad and are preferably disposed in the corners of these flat plates. The o-ring is slidably received between the at least one projection of the cage and the central portion of the cage so that the cage is axially fixed with respect to the shaft. The conversion of the compound from the crystalline form to an amorphous form can be effected by laser exposure. Additional information such as average gradient could also be saved in the table.