For books and other bound work, the grain should run parallel with the binding, creating a smoother fold, making the pages easier to turn, and allowing the paper to swell across the grain. If the binding runs across the grain, the free ends of the paper will swell or shrink with moisture changes, but the bound ends will not. The book will buckle and the binding will weaken. With sheet paper, the grain direction is indicated by underscoring the dimension along which the grain lies or by changing the order of the numbers. On web paper, the grain runs along the length of the paper web.
Fibers line up parallel to the long side of the paper.
This book in your hands is an example of grain-long binding. Fibers line up parallel to the short side of the paper. The image carrier, which is flat or cylindrical, moves through an ink pool. A blade scrapes excess ink off the plane of the plate, leaving ink in the recessed wells. A second cylinder presses the paper onto the plates, where it picks up ink from the wells.