Note: We are using the word “version” in this section because technically, the modified version of a file in your working copy does not belong to a revision until you commit your changes.
When you select “Compare Differences...” from the “Action” menu, a dialog opens to select which two versions of the same file to compare. By default, the original version in the working copy —the BASE revision— is selected on the left, and the modified file in the working copy —the version that's actually in your working copy— is selected on the right.
Use the “Compare Differences” dialog to select and compare any two versions of a file.
A list of other revisions is shown in the table below the popup menu. Choose “Existing revision in Repository:” from the popup menu to select a revision to compare with in the table below it. Finally, click the “Compare” button to compare the versions selected on the left and right with eachother.