This command is found on the Home tab as well as the View tab of the ribbon bar. When WinList is configured to use the classic toolbar and menu interface, the command is found in the Window menu.
Scale to Fit adjusts all data source windows proportionally to fit into the main application window. The command automatically scales the histograms of each data source to fit the new space of the data source, too.
You can click the down-arrow on the button to select Scale to Fit for histogram windows in the current data source.