QuiltE, you select a fabric type...woven light, med or heavy...knit light, med heavy...vinyl,leather and the Sensor System selects the needle to use, stitch length, tension and actually senses the fabric so that the presserfoot has the correct amount of pressure on the fabric as it's being sewn...what I love is that when you stop sewing and the needle is in the down position the presserfoot lifts about 1/8" and you can pivot if you need to ...better yet is when you're sewing and stop you don't have to use your hand to raise the presser foot...you just sew off the piece and tap the foot pedal and the foot raises so you can remove it. or press the cut button and the machine pulls the thread to the bottom and cuts the thread and lifts the presserfoot...Voila!!!! The Sensor System..