The gauge is percent completed for all files (bytes completed / bytes counted if you have the tick mark activated)

Bytes are counted based on the left window contents, and the comparison is made searching for * these and only these * files on the right window directory.
Symbols are for the files on the left.

e.g.

Files on the left are:
temp1.txt	2000 bytes
temp2.txt	1000 bytes

files on the right:
temp1.txt	2001 bytes and more recent.
temp3.txt	x bytes

Report will be:

< O  temp1.txt
!    temp2.txt 





Symbols are:

<	Left file smaller in size.
>	Bigger.
<>	Same in size but different in content.
O	Older.
N	Newer.
!	File or Dir not found.

Directories not found are reported but * not * the files and dirs under it, although they are counted on the main window counter ...
