Fish finders

Ive recently aquired a "Fishin Buddy 1"side viewing fish finder.The problem is i dont know the meaning of the inverted V symbols.
Does one bar mean one fish or several small ones?
When you activate the large /small selector buton what is the calibration,
ie Small fish =fish to 6oz?
Large fish starts at what size?
I would be very gratefull if some one could help me out please.

Gordon Braithwaite
Withnell Angling Club

Ive repaired a couple of these units and I think they are made by BOTTOM LINE do a search Im sure they will help .
If I find the site I will post it on.