Remember reading about this ...damned if i can remember where though sorry lol! Try a search on here or minelabowners.com has to be one of them.
As far as i recall it's a hidden screen used by factory engineers for reprogramming and checking faults etc.
here is the info for the explorer machine but the key sequence is unknowen
hidden screen on the e-trac
this is Supposedly how you are meant to access it.
"To access the 'Expert' screen, press Menu>Expert> scroll down to select "Ground" and then press the Left arrow (below the on/off switch.)"
You must press the Accept/Reject button to initiate the analysis.