I have noticed with some clip on tuners that sometimes they do not respond to low frequencies , on my Snark's is a bit that way . The black one and it is afew tears old , so not sure of the model . Have found if you play the open string harmonic at the 12th fret, it responds straight away . For beginners , lightly rest your finger on the string at the 12th fret and pick it , you should hear a ring , this is a harmonic of the open note , tune the string to that .