Tracing wheels are a great tool that sewists use instead of pens, pencils, and markers. The serrated blade leaves a perforated line on your fabric as you trace the wheel around the pattern. You'll never have to worry about bleeding, smudging, running die, or dried-out markers.
This tracing wheel includes an additional blade that you can use to mark your seam allowance. Each blade is reversible and can be moved left or right depending on the seam allowance you're trying to achieve. Seam allowance marking ranges from 0" to 1".