Use Query|Annotate to view the 'history' of the selected file on a per-line basis.
Similar to the Log command (see Log), you can configure the period of time for which the annotated view shall be calculated.
On the Advanced page, select Track content of all revisions to have the file contents of all revisions present for the subsequent Annotate window. Otherwise you will only be able to see the content of the latest revision for the selected file.
Use Treat even binary revisions as text to continue the Annotate even when it encounters one or more binary revisions of the file. This option can be necessary if the MIME-Type of a file had been corrected e.g. from binary to text in some earlier revision, although the file had text content since ever. In case the file actually had binary content in some earlier revision, parts of the annotate output might be trash.
After performing this command, the Annotate window for the selected file will come up. For details refer to Annotate.