You can compare a changeset item with:
Another revision of the same item.
A work file on disk. This option is only available when the corresponding file exists on disk and is part of the currently open solution.
Another item revision in the repository.
To compare a changeset item:
Open the Changesets view.
Right-click a new, imported, or modified item and do one of the following:
To compare with the previous revision (if one exists), select Compare with <item revision>.
Select Compare with. The Compare Items dialog box appears. Do one of the following:
• To compare the revision with a different revision of the same item, select it from the Another Revision list.
• To compare the revision with a file in your work area, select A workfile, click the Browse button, and navigate to the file.
• To compare the revision with a revision of a different item in the repository, select Another item, click the Browse button, and use the Select Item dialog box to search for it.
Click OK. The items are opened in the default merge tool.