Sheeting

To add sheeting allowances to a plot, simply enter the desired sheet thickness into the "Sheeting" box. Typically you'll enter a small number or fraction here. If you specify sheeting that is too thick, you'll get an error alert.

If sheeting is specified, the original airfoil will be plotted as a dashed gray line, and the new, inset airfoil will be drawn in solid black.

I don't know why you'd want it, but negative sheeting is allowed: this will "outset" the foil instead. Perhaps for wire kerf allowance on the top surface?