Many booklet stamps can be identified by one non-perforated edge, though a few are perforated on all edges. On booklets up to 1977, the printing plate construction enabled both upright and inverted watermarks in equal quantities owing to a gutter dividing rows 6 and 7 in the sheets of 12 × 10 stamps. The gutter was used for stitching during assembly, requiring rows 4–6 and 10–12 to be turned through 180 degrees so those panes could be stitched on the left of the booklet.