I feel like I've asked this some time ago, but can't find it, so sorry!

I need a way to uncover the difference (one or two cells I suspect) between
an old version and new version of the same massive file. I seem to recall
you folks had some way to do this, perhaps some add-in created by one of
you. Can anyone remind me?

Is there any danger in these 3rd party add-ins?

Thanks!
Dean