Differential feeding is a mechanism on coverlocks and overlockers that controls the movement of fabric using two separate feeders, front and back. These feeders can move at different speeds. The ratio of their speeds is set on the machine control, usually indicated by numbers. The front feeder can move faster than the rear feeder, which causes the fabric to bunch up, or slower, which stretches the fabric slightly and prevents the seams from rippling. Alternatively, both feeders can run at the same speed, which is a neutral condition.