Chromatic Tuner Display Basics
Electronic chromatic tuning devices display pitches in several ways. These display types are used throughout the many models of tuners. We will define them first before explaining the other features.
Needle Tuner
Needle tuners use a needle, either LCD or an actual analog needle, or a similarly-functioning row of lights. Lights may be used to give additional feedback, for example a single green light glows above the needle when pitch is matched. The displays indicate the sharpness or flatness of the note. If the needle or lights position themselves to the left of center, the note is flat; to the right, sharp; middle, in tune. The most economical tuners use the LCD needle or its variants. Tuners with actual analog needles are the most accurate visually among the needle-based chromatic tuners. An advantage of needles--especially actual analog needles--over strobes is the ability to read directly how many "cents" off a pitch is (cent is the unit used in pitch tuning). LCD needles, however, may not have the resolution to show fine differences.
Strobe Tuner
Strobe chromatic tuners use the best type of display for adjusting a note visually. They use spinning disks or a horizontal line with moving patterns of light and dark; if the pattern moves left, the note is flat; the faster the spin or movement to the left, the flatter the note. If it spins to the right, the note is sharp. When the pattern stops moving, the note is tuned. A display that changes speed can be easier to tune to precisely than seeing if a needle lines up perfectly with an index line. Strobe displays using discs need to be serviced periodically. Note that not all tuners with circular displays are true strobes. Some other tuners arrange their LED lights in a circle, but they simply light up left or right of center, without any change in speed, which is really needle display.