Because of their ubiquity, and the fact that they have an adjustable hertz setting, I would hypothesize you're using a Korg chromatic tuner. That is not to say that they're the only tuners with a hertz calibrator, but you could understand my assumption. Anyway, if that is indeed the tuner you are using, you'll want it set to 440Hz because as Lewis said, it is standard among chromatic tuners, and what 99% of all music is tuned to. Wow, that was a long response for a simple question.