How do I identify & remove unused Slide Masters in presentation?

[Bubba]

I see many slide masters in the Slide Master View, but I can't tell which
ones are in use. There also appears to be duplicates. I simply want to
clean up the view so that I can make changes to the appropriate Slide Master.

 

[Mark]

I see many slide masters in the Slide Master View, but I can't tell which
ones are in use.  There also appears to be duplicates.  I simply wantto
clean up the view so that I can make changes to the appropriate Slide Master.

If you hold the mouse over a layout or slide master, it will display
which slides are using that layout/master.