Try this in TextEdit, or any Cocoa app (make sure that “Check Spelling as You Type” is enabled).

1. Type “/gauge ” (no quotes; that’s the word “gauge” with a slash before it and a space afterwards).
   
   

1. Control-click on “gauge”. You’ll see the regular Cut, Copy, etc menu. The word will also be highlighted.
   
   

1. Now click outside the word, without choosing any of the contextual menu options. A red wiggly underline will now appear under “/gauge”.
   
   

1. Control-click “gauge” again, and look at the suggested replacements. You may have to repeat steps 3 and 4 if you don’t see the list.
   
   

Can anyone explain what those replacements mean?