is the Tcl/Tk GUI interface to CVS. It also has online help. Try the following:
Click on foo.cpp
Click on 'Revision Log Icon' which is located next to 'spectacle' icon.
This will display the branch TREE in the window. Now click the RIGHT Mouse
button on the text '1.3' and click the LEFT Mouse button on text '1.1'. Then
click on "Diff" button. This will display a two-pane window!!
Click on the "Next" button to step thru more diffs.
Click on "Center" to center the text.