[TenTec] O-2 Screen Lines

[K5XS at aol.com]

This is truly fun.  I am figuring out the radio and trying to discover  every 
little nook and cranny on it.
 
One thing has me puzzled, and I can't find it in the manual.
 
Immediately above the spectrum sweep scope is a horizontal line on which  the 
rectangles representing the bandpasses for the main (left) and sub (right)  
receivers rest.  The line has a break in it, and it is decidedly off center  
(to the lest a bit).
 
Does that line represent something?  Does the break represent  something?
 
Thanks
 
Bernie K5XS