How to read the tuner
The big letter is the note the tuner hears, the small number next to it is the octave (A4 is the A above middle C). The needle shows the distance to that note in cents: one cent is a hundredth of a semitone. Left of the middle means the note is flat, so tighten the string; right means sharp, so loosen it. Within 5 cents the display turns green, which is closer than most listeners can hear.
The hint under the needle tells you which way to turn and the exact target frequency. Turn the peg slowly and let the note ring: the reading settles after a fraction of a second.
Presets and the chromatic mode
With an instrument preset, the tuner compares what it hears with the nearest string of that instrument and highlights it. If a string is very far off, for example a new string that is a whole tone low, press its button to lock the tuner to that string, and press Auto to go back. Play reference plays the target note of the highlighted string, handy for tuning by ear.
Chromatic mode shows the nearest of all twelve notes, so it works for any tuning, for wind instruments, for a piano check or for singing. Choose between letter names (C D E) and Do Re Mi in the Notation menu.
A4 reference: 440, 442 or 432 Hz
Almost all modern music is tuned to A4 = 440 Hz. Many orchestras tune slightly higher, to 442 or 443 Hz, and some musicians prefer 432 Hz. Set the reference to match the band, the backing track or the piano you play with; every note and string target moves with it.
Tips for a steady reading
Tune in a quiet room and hold the instrument close to the microphone. Pluck with the fleshy part of the finger rather than a hard pick attack, and mute the other strings. Laptop microphones handle guitar and ukulele well; for the lowest bass notes a phone or headset microphone held near the instrument often works better, because small laptop microphones barely pick up 40 Hz. Plucked strings start slightly sharp and drop a little as they ring, so read the needle after the first moment.