Bernina Foot Number 20

I recently acquired Bernina Foot Number 20.  It is designed as an embroidery foot. I find it very useful when sewing darts. The dart point is clearly visible. I think it will help in the accuracy of buttonholes. It is sometimes referred to as an open toe foot. What distinguishes it as an embroidery foot is the groove on the under side of the foot. It is wider than the standard foot to accommodate larger areas of satin stitching.