A calibration apparatus is provided for adjusting the relative phase between two signals received at a memory chip, the two signals being generated such that they are synchronized with one another in a controller and are transmitted to the memory chip via separate lines. A recessed portion recessed inwardly of the cover is formed in a part of the cover corresponding to the part, to which the center of pivotal movement of the element unit is displaced, through a stepped portion. The signal can be coupled to eliminate offset shifts due to component mismatches, calibration, aging andor temperature associated with the sensor device. In the expanded state, the channels provide a fluid conduit along an area between the screen and the wall of the wellbore. A lifting mechanism within the tube raises the vertically oriented platform assembly up within the tube.