The Chaco Liner is useful for drawing thin lines on fabric. With a mini-rotating wheel (similar to a pattern wheel), chalk drops onto your fabric as you roll it across your fabric.
Sue Garman uses a Chaco Liner for marking quilt designs and lines on quilt tops - as well as for marking other stitch lines when she appliques. The markers are easy to use with little applied pressure. Sue does not recommend any color except white when marking fabric with a Chaco Liner.