Guitar & Ukulele Tuners
A needle, LCD or regular LED type guitar tuner uses a microprocessor to measure the average period of the waveform. It uses that data to drive the needle or array of lights. When the musician plays one note, the tuner senses the pitch. The guitar tuner then displays the dig in relevance the required pitch and indicates whether the input pitch is lower, higher, or equal to the desired pitch.
With needle displays, the note is in tune when the needle is in a 90° vertical position, with leftward or rightward deviations indicating that the note is flat or sharp, respectively. Tuners with a needle are typically furnished with a backlight so that the display can be read on a darkened stage. For block LED or digital display tuners, markings on the readout drift left if the note is flat and right if the note is sharp from the desired pitch.