I can tune a guitar to itself pretty easy, but I'm not quite as lucky with concert pitch. I can get it close, but not there. In my dorm there's a guy named Andrew, a music major who is driven insane by the fact that my guitar is almost always out of tune. He'll stop by about once every two days or so, gripe at me for it and put it perfectly in tune by ear, without even using the other strings for reference. Then I'll put it in open G for slide and back and it'll be intolerable to him again. And so the cycle continues..