This operation is only available in the right-click menus of scatterplot trellis displays and sum-difference plot trellis displays. What it does depends on if there is a ✓ mark to its left in a right-click menu.
It adds a lowess curve to the point cloud in each panel of a trellis display.
If the Shift key is pressed when this operation is invoked, a dialog will pop up for you to specify smoothing parameters. See Add Lowess Curve for details.
If a trellis display has any panel plots, this operation will add a lowess curve to each of them, too. Unlimited panel plots won't be affected.
Lowess curvers are already being displayed in the trellis display on which this operation is invoked and in any associated panel plots. This operation will remove all these lowess curves.