Guitar tuner

It measures the pitch you play and compares it, in cents, with every string of the selected tuning, then tunes you towards the closest one. That works as long as a string is less than about half-way to its neighbour. A string that is badly slack — say your low E sits nearer to D — will be matched to the wrong target, so tap the string you are actually tuning to lock it; the needle then measures against that string only, and tapping it again returns to auto-detection.

A cent is one hundredth of a semitone, so the needle's range of −50 to +50 covers half a semitone either side of the target. The reading turns green within ±5 cents, which is tighter than most listeners can hear on a single note. For chords that ring cleanly, aim for the needle to settle in the middle of the green band rather than at its edge.

Pluck one string at a time and mute the others with your fretting hand — a tuner can only follow one pitch, and ringing sympathetic strings confuse it. Pluck firmly but not so hard that the string slaps the frets, and give the note a moment: the first instant of a pluck is noisy, and the reading steadies as the string rings. A noisy room, a fan or a phone speaker playing music will also keep the tuner from settling.

Use 440 Hz unless you have a reason not to: it is the international standard and what almost all recordings, keyboards and other tuners assume. Change it only to match something else — an orchestra tuning to 442 or 443 Hz, a piano that sits a little flat, or a track recorded at 432 Hz. The setting moves every target together, so the strings stay in tune with each other at any reference.

Yes. The 4-string bass preset targets E1 A1 D2 G2 and listens down to about 32 Hz, and the ukulele preset uses standard re-entrant G4 C4 E4 A4 tuning. For anything else — violin, mandolin, banjo, a 5-string bass or a voice — choose Chromatic: it names whichever note you play, with its octave, and shows how far you are from it. Very low notes such as a 5-string bass's low B are near the limit of what laptop and phone microphones pick up.