Abstract

To determine machine-direction variations in measurements of a travelling sheet during production, the sheet is repeatedly traversed with a scanning sensor and, during each traverse, measurements are taken at a plurality of locations. Then, a series of reference slice locations are selected which extend in the true cross-direction. For the reference locations, measurement values are estimated based upon actual measurements. Then, for each scan, the average of the estimated measurement values is calculated. Next, cross-directional variations in values at each slice location along selected scans are calculated by subtracting the average value from the estimated value at each location along the scan. During the next consecutive scans, machine-directional variations in the sheet property at slice locations are calculated by determining the difference between the measured value and the calculated cross-directional variation value for that slice location along the prior scan.