The length of the book is measured using the MEASUREpHASE, and to this measurement 8 mm is added, to allow for 4 mm of square at both the top and bottom. This amount of square is more generous than the usual 3 mm because the edges of the text block's leaves are uneven. This is due to slight variations in the locations of the holes, rather than to varying dimensions of the leaves. Because of this, trimming the text block in the guillotine while it is out of the binder will not align the edges flush when the structure is reassembled, so we compensate by adding an extra millimeter of square.