Sorry, you wanted to know what it does. Here is what the manual says.
1. Place the fabric inposition under the presser foot.
2.Start sewing. The machine will sew the tapered point and then continue with a satin stitch at the selected stitch width. A reverse icon is shown on the Graphic Display indicating that you need to press the Reverse button to step to the next part of the stitch. When the satin stitch is as long as desired, press the Reverse button. This will start the tapering of the end. When the tapering is completed the machine stops automatically.
3 To repeat the stitch with the same size, press the STOP button. Reposition your fabric, then step on the foot control to sew again. The machine will stop automatically when the stitch is completed.
I hope this helps you.