A portable stand alone treatment station for eyes which have been exposed to corrosive liquids, noxious gases and foreign objects. The measurement system comprises a compressible waveguide, ultrasonic transducers, and circuitry to sustain energy wave propagation in the waveguide. The correction value calculating means 7 calculates a correction value on the basis of the thermal displacement estimated by the thermal displacement estimating means 5 alone when the main spindle 15 is started up and rotated.