Play the string of viola to the microphone that you want to tune, and watch the indicator on the screen blink and move to correct string position.
if triangle is pointing to the left of string you play, that means you should tighten it.
if triangle is pointing to the right of string you play, that means you should loosen it.
The tuner reacts faster and more accurate if the microphone is placed closer to the string.
Touch the other strings with your fingers to prevent them from producing sound and disturbing the measurement.