In a system for monitoring an output of a sensor for detecting an operating state of a gas turbine engine by comparing a value of an output of the sensor with a prescribed reference value, a calibration map for converting the output of the sensor into a variable that is normally used for controlling the engine is used for defining the reference value for determining the state of the sensor. The method continues by providing a test input to the programmed circuit. Rear parts of the guide bars 15 are secured to an adjusting plate 32 which is provided with a positioning means 60 for adjusting and holding a distance S between the driving plate 31 and the movable platen 12. The pattern includes a plurality of linear protrusions or grooves that extend in a wave shape in a tire circumferential direction while deflecting in a tire radial direction with a period of \u03bb1.