Section 3.1 Accessing the 2D Trace Plane
Although the 2D Trace Plane will sometimes be displayed automatically (e.g., when displaying contour plots), it is generally not displayed when you first open CalcPlot3D.
To access the Trace Plane, click on the trace plane button, located at the far right of the row of buttons above the Add to graph menu. See the circled button below.
