At the top of the pedal there is an LED display that identifies the note that you're currently playing.

The beauty of the TU-2 is the bright LED display, as well as its accuracy with direct input, and the fact that it's always THERE for you to use, if you leave it in your pedalboard.

It should be noted that as of Jan. 2010, BOSS now makes the TU-3 tuner, which is supposedly more accurate and has a more precise LED display.