 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 . 
