Stitch density is a measurement of the number of needles that enter a square centi-meter (in the metric system) or a square inch (in the imperial system) of fabric as it passes from the entrance of a needle loom to the exit. It is determined by the number of needles in the boards, the number of strokes of the loom, and the advance (distance traveled by the fabric) per stroke. A modern loom will have a computer readout for this number. You usually have to tell the computer how many needles per meter are in the boards when you first install the loom. After that it will continuously keep track of the stitch density and display it on the screen. Stitch density is important because it tells you how many needles are going into the material. Multiplying stitch density times the number of barbs going through the bed plate will give you the total number of barbs that are effectively needling the material.