Normalization isn't done internally by MP3 Diags; instead, an an external program gets called to do the job. MP3 Diags is meant to work with MP3Gain, but it will probably work with others, although the displayed info might be wrong. By default it is configured to call MP3Gain. It assumes MP3Gain is in the execution path and that you want to do normalization in album mode. Otherwise, you'll need to go to the
configuration dialog and adjust some settings.