Comparison Management Options
The Diff and Merge menu includes a series of commands that are used to customize the file and directory comparisons and can be summed up as comparison management options. Apart from the option to explicitly start a comparison (see below), options to automate certain comparison functions as well as to facilitate the selection of recently compared pairs are available.
Starting a comparison
The Start Comparison command in the Diff and Merge menu applies to File Comparison as well as Directory Comparison windows and is used to explicitly start a comparison at any time. Please note that a comparison starts automatically and this command is thus not needed if the Autostart Comparison or Compare while Editing comparison management options are toggled on.
To explicitly start a comparison:
•Select the menu option Diff and Merge | Start Comparison or press F5. Alternatively, you can also click the corresponding toolbar button 
in the Diff and Merge toolbar or right-click the tab of a comparison window and select the Start Comparison command from the context menu that appears.