A calibration procedure is carried out for determining the displacement distance from a reference point to the center of the blade in a web cutter in a mail inserter. A photosensor is placed near the paper plane of the web cutter to sense a web edge at the reference point downstream or upstream from the blade. At the start of the calibration procedure, the blade is caused to cut the web for providing a web edge. The web edge is moved in a backward and forward motion over the photosensor a few times for determining the theoretical center position of the photosensor relative to the position where the web is cut by the blade. By taking into account the chip-out width, the displacement distance from the center of the photosensor to the center of the chip out blade can be determined.