Click the Edit button on the Function Name Manager dialog (after selecting an existing 3D custom function) to display the Edit 3D Custom Function dialog.
Range. Use the Range group box to specify the ranges (i.e., Minimum and Maximum values) for the custom function in the two horizontal (x and y) dimensions. Note that additional options for controlling these ranges are available in the Graph Options dialog - Custom Function (3D XYZ Graphs) options pane.
Function guide. Select the Function guide check box to display a list of possible functions and related properties when you enter a custom function into the Function box.
Function