An optical displacement measurement apparatus increasing the valid light receiving area struck by light so as to give a larger signal and reducing the effect of any unevenness or spottiness of the illuminance of the light source or any scratches or dirt on the glass scale is provided. The information content of the feature vector components which is at least necessary to ensure the speech recognition rate is determined using a stored speech recognition rate information. Furthermore the device is embodied for detecting the end of the movement of the valve piston in the valve if the first variable is greater than a predetermined first threshold value and the second variable drops be low a predetermined second threshold value. The characterizing data characterizes known heights of the measurement points. The second comparator receives the periodic signal and compares the periodic signal with a first threshold voltage to generate a second output signal. The icewalker comprises a flotation base, a moveable rod connected to the underside of the base, a flotation arm attached to the rod containing a flotation arm skate and culminating in a spike at one end, a plurality of flotation base skates and a line attached to the bottom of the rod at one end and whose other end passes through an eyelet which is attached to the underside of the flotation base.