Yeah, a friend of mine has a GA-30. If his is any indication, those are very frustrating tuners. He says that his sometimes goes to 7b and switches rapidly to 2b, back and forth fast. Either way though, it should work out. A b is a b, as far as your tuner knows. If you tune it to the 7b, it should sound the same as 2b. Hope this helps. :)

P.S.- apparently these tuners can't even tune to drop D,or anything that isn't standard. If I were you, I'd look into the CA-30 chromatic tuner (chromatic means you can tune to any note), I have one and it has never failed me.