A perfect stitch on knit, no wave or distortion, all thanks to differential feed.
So what is differential feed?
In order for a machine to have differential feed, it must have two sets of feed dogs. All home sewing machines only have one set of feed dogs; therefore, home sewing machines cannot offer differential feed. All the sergers we choose to carry have two sets of feed dogs, and do offer differential feed.
Like the name implies, differential feed allows you to differentiate how fast each set of feed dogs feeds the fabric. By having one set of feed dogs feed the fabric faster than the other set, you are able to feed the fabric in such a way that prevents the knit from being stretched as it is fed through the machine. Consequently, you prevent the machine from making a stitch as the knit fabric is stretched out, and avoid the wave/distortion problem.