A 12-string guitar has six pairs of strings. On the four lower pairs (E, A, D and G) the thinner partner is tuned a full octave above its main string, while the B and high E pairs are tuned to the same note. With two notes ringing an octave apart, a normal tuner often shows the wrong string or jumps between two readings.
This tuner knows all twelve strings. Guided mode walks you through them in order: pluck one string on its own while a fingertip keeps its partner quiet, bring it into the green, and the tuner moves on by itself. Each string chip shows the exact octave it should be in, so a partner tuned to the wrong octave is caught straight away.
Two strings can each read as in tune and still sound slightly sour together. The pair check fixes that last step. Strum both strings of one pair, and the tool listens for the slow wobble, called beats, that happens when two notes are a little apart. It shows how many beats a second it hears and roughly how many cents apart the strings are. Turn one peg until the wobble slows and stops.
Pick standard, half-step down, whole-step down, drop D or open G for 12-string, set a capo, and tap any string to hear it played back.