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You can adjust the mapping range of a dataset that has already been displayed in the graphical window. This is done by clicking the 
icon in the toolbar, and then clicking on the graphical element in the graphical window. The Range Controller menu will appear and show the data scalar range and the min and max value which the color table has been mapped against. You can change these values by using the up and down arrows on your keyboard, or by dragging the sliders in the menu.