When sewing with patterns that do not have seam allowances, this tool quickly adds in the allowance when used in conjunction with tracing paper. The dual heads swivel out to trace, and swivel in to store, plus adjust to different widths for various seam allowances. This is a great gift to give the young tailor or fashion design student in your life, or to give yourself if you want to be creative and make adjustments to patterns. From Clover.