The double tracing wheel is a handy little marvel. With it you can trace off your cut lines and seam allowances in one easy motion. It can also be used to increase or decrease the size of a pattern piece. The wheel position is adjustable so any seam allowance from 1/4" to 1 and 1/4" is selectable. Because the two wheels are held together on the same handle the resulting lines will be perfectly parallel every time.