PURPOSE: To determine the accurate position correspondence relationship between the thickness measurements of a sheet in the cross direction and slice bolts by subjecting the former measurements to power spectrum analysis to determine the peak frequency or the like.

CONSTITUTION: A paper stock-issuing slice lip is provided with many bolts along the cross direction, and in determining a position in the cross direction affected by the tightness of a certain bolt through measuring the cross direction profile of the thickness of a sheet afforded by papermaking of a paper stock issued from the slice lip, the following procedure is performed: (A) the sheet is divided into a plurality of sections, (B) thickness measurements for the respective sections thus divided are subjected to power spectrum analysis to determine the peak frequency, (C) based on the peak frequency, a smoothing constant for smoothing the measurements is determined, and (D) based on the smoothing constant, the aimed position correspondence relationship between the above slice bolt and measurement point is determined.