PURPOSE: To improve the accuracy in estimating the thickness distribution of the charger layer in a furnace with a less number of measurement with a profile memter by making use of the depth (index) obtd. by detecting approximately continuously the descending condition at one point on the surface of the charge in the furnace near the wall of the furnace top separately from the depth measured with a top profile meter.

CONSTITUTION: The calculation depth YCn.i of the charge corresponding to the depth at the i-th point of the optional n-th batch by a furnace top profile meter S is calculated by the equation and the calculation is seccessively repeated, by which the profiles on the surface and bottom surface of the charge are determined. The average layer thickness distribution at every charging is then estimated. In the equation, aWd: constants, xn.i: the coordinate in the radial direction in the furnace, Zn: the sliding amt. to be determined with each charge, k: the constant of a descending speed distribution, R0: the radius of the furnace port, Rs: the radial distance from the furnace wall to the measuring point with the meter S, ΔSn.i: the index descending amt. of sounding at one point from the stage of charging up until measurement.