Crop marks

Crop marks belong to a set called printer's marks: crop marks for the cut, bleed marks for the edge of the bleed, registration marks (a crosshair in a circle) for lining up the printing plates, and colour bars for checking ink. They are drawn outside the trimmed page, so the PDF page is made larger than the book and the finished size is recorded in the file as the TrimBox. The marks start beyond the bleed — usually 3 mm (0.125 in) past the trim — so that a slightly off cut never shows a line on the page. On a black-and-white interior they are usually set on the black plate only, which keeps the colour plates empty.