Guitar tuner's interface is pretty intuitive, if your instrument is sharp the sharp side will light up if it is flat the flat side will light up. There are no preferences, or buttons to push. Guitar tuner listens through your default sound device, if your having trouble getting it to respond, try turning up the gain on your default device. This is done in System Preferences -> Sound for the built-in microphones.
What's new in this version:
Updated to be compatible with newer versions of Mac OS X.