The present invention relates to systems and methods for calculating the additional local stretching of a moving web through a converting process in order, during rewinding, to find the position of defects in the web that were identified during winding and stopping the web with the web defect close to or at a defect correcting station. The method comprises, during rewinding of the web, the steps of detecting position markers (PM(n)) applied during winding of the web (5), measuring the distance between the position markers, calculating the additional local stretching between the position markers occurring during rewinding, applying the calculated additional local stretching to the known position of a following web defect to determine an estimated position of that web defect in the rewinding web. A method for correcting a web defect comprises the step of subsequently stopping the web with the web defect at, or close to, a defect repairing station (38).

Machine for controlling the shape of a reel of web product, comprising a pick-up zone for at least one reel to be evaluated, a moving apparatus of said at least one reel from said pick-up zone to an unloading zone, and an evaluation apparatus of at least the outer diameter of the reel, configured to act between said pick-up zone and said unloading zone.