I recently changed the battery in my Korg AT-2, and somehow have succeeded in changing the settings.

When I switch it on, both diodes flash on and off simultaneously, and when I play a note which I know to be correct at A=440 concert pitch, it indicates that the note is sharp, suggesting that I have inadvertently recalibrated the tuner to a different pitch (which I do know is possible with this model )

Unfortunately, I have long since lost the instructions that came with the tuner, so it would make my day if anybody out there can tell me how to get the thing back onto concert pitch.