D'Addario PW-CT-21 NS Micro Clip Free Tuner
The ultimate in discreet tuning, the NS micro clip-free tuner features a full-color display and metronome in a housing that blends with the aesthetics of any instrument. The included clip-free mount attaches directly to your instrument’s tuning machine (screws included) so your tuner is always at hand and visible only to you.
D’Addario electronic tuners are designed by musicians for musicians featuring intuitive features, easy to read display, and exceptional tuning accuracy.
It's a bit hard to explain so check out D'Addario's own video for this tuner below if you want a bit more information!