The Audio Technica Stroboscope Disc & Quartz Light helps you monitor your turntable rotation speed. You will get both a stroboscope disc for placement on the spinning vinyl & a quartz strobe light device for reading your stroboscope disc. These helpful tools make achieving a more accurate playback speed simple. The quartz strobe light features a yellow LED built-in helping you obtain a clear reading of 33 1/3 45 & 78 RPM speeds on the stroboscope. If your turntable speed is accurate the markings on the stroboscope should appear to be stationary. A helpful overhang guide on this Audio Technica stroboscope makes reading the markings easier.