Abstract: A headbox (10) has a stock inlet header, a tube bank, a tubulence generator and a slice channel. Measurement targets (PA, PB, PC, P, PE) are provided with means for making measurements of the fiber mobility of the fiber suspension, then controlling the flow state of the suspension. Sensors on the width of the headbox (10) or traversing sensors are positioned on different width points of the headbox (10) and arranged to measure the fiber mobility profile, with means for changing the flow state on the basis of the measurements. Apparatus for diluting the thick stock into headbox consistency and units for cleaning the stock to be fed into the headbox may be provided. Sensors may be disposed in the short circulation pipes or cleaning units arranged to measure the fiber mobility of the fiber suspension with means for changing the flow state on the basis of the measurement data.

Abstract: Streak defects in web structures are characterized by electronically obtaining a plurality of results of a plurality of tests of a web structure, electronically determining a location of and/or a quantification of one or more streak defects based on the plurality of results, and electronically characterizing the streak defect(s) as being static or stochastic based on the plurality of results.