are you talking about on the secondary eicas page? Is it a little blue message on that page in the bottom right corner? I couldn't find anything in any of my manuals regarding that phrase. However, the pilot manuals don't list the maint. messages displayed on that page, so I'm guessing a 57 mech would know better. I'll ask around for ya
Now that I think about it, the comparator bite message is displayed on the status page of the lower EICAS screen prior to the IRS alignment. The ADI's use IRS info for alignment. The comparator monitors both ADI's and displays an EICAS message if they're off by about 4 degrees between the two.