Measuring less than 3", the Speed-E fits in the palm of your hand and allows guitarists and bass players to instantly tune any "E" on their instrument. There are 2 ways to tune your guitar using the Speed-E: tune the open "E" strings using the Speed-E and tune the other strings by ear, or tune the entire guitar with the Speed-E by fretting an E on each string. Red and blue indicators indicate flatness or sharpness, and more than a half-step off gets a flashing response.