One accidental flaw in line perforation is irregular or wavy perforation. This type of anomaly is a specific risk of line perforation machinery; unlike comb perforation, where the grid is fixed, line perforation processes each line independently. This flaw occurs when the sheet of paper is not perfectly aligned or shifts slightly during feeding. If the paper moves while passing under the perforating needles, the needles strike in a curved or wavy path rather than a straight line, resulting in a structural dislocation.
1945 Split Provisional Issue, block of four showing a distinctive misplaced and curved perforation on the left margin. The upper part of the vertical perforation deviates by 2.3 mm from the true vertical line, resulting in a pronounced irregular curvature. An attractive and rarely seen perforation error.
