GB_Amateur, I can take a speculative shot at this, having been a pretty long-time FBS user.   I am going to guess that this X,Y screen is FE in the vertical (y-axis) and CO in the horizontal (x-axis).  The horizontal line across the screen is probably similar to the "12-line" on an E-Trac or CTX.  What the 12-line means is that when moving from the Explorer series (where FE numbers were different for each different target), they were "normalized" for "good" targets to a "12" FE nu