I have another question.

This Yamaha didn't sound right one night so I thought it's out of tune. I put the tuner on it and it should have been in perfect tune, but it still didn't sound right to me. I ended up breaking the top string. The guy at the guitar store put a new string on it for me (just that one string) and it sounds ok. I asked him to check the neck and make sure I didn't hurt it since it was the top string I popped, he said it was fine. He tuned it too, I got it home and thought well maybe my tuner is broke so I decided to see how it read while I knew it was in tune. The needle gets close to E (left side of E) then it bounces to D and goes all the way to the left. It does this everytime so I put the tuner on the new guitar and it didn't do that. My question is what would make it do that? It just does it on the top string, the one I broke. I'm scared to death that I hurt his guitar!!