Adding an operator
When you add an operator to a plot, the name of the operator appears in the plot list entry to the left of the variable or any previously applied operator. If you apply an operator to an already generated plot, the plot is regenerated immediately with the applied operator. If a plot has not yet been generated (its entry is green), then the operator does not take effect until the plot is generated. This provides time for setting the operator attributes.
It is also possible to apply an operator by clicking an operator attributes window's Apply button. If you click the Apply button when there is no operator of the specified type has been applied to the selected plot, you can apply the operator and any changes you made by clicking the Yes button in a dialog window (see Figure4-3) that asks whether or not the operator should be applied to the plot.