Three of the Scatter plot's four input variables can be set in the Scatter plot attributes window. The first input variable cannot be changed from within the Scatter plot attributes window because that is the default variable used by the plot. If you want to change the first input variable, you can use the Variables menu under the Plot list. If you want to select a different variable for any of the other input variables, you would first click on the input variable's tab and then you would select a new variable by making a selection from the tab's Variable button. Note that any combination of nodal and cell-centered variables can be chosen. The Scatter plot will recenter any input variables whose centering does not match the first input variable's centering.