Guitar chord in the abstract musical-theory of chords for all instruments. For example, in the guitar (like other stringed instruments but unlike the piano), open-string notes are not fretted and so require less hand-motion. Thus chords that contain open notes are more easily played and hence more frequently played in popular music, such as folk music. Many of the most popular tunings—standard tuning, open tunings, and new standard tuning—are rich in the open notes used by popular chords. Open tunings allow major triads to be played by barring one fret with only one finger, using the finger like a capo. On guitars
Tuning mechanisms for stringed instruments not yet learned to tune precisely using pegs alone. Pegs for double bass and guitar family instruments are usually geared, and are called tuning machines or machine heads. They often use a worm gear. The gearing ratio varies; while higher ratios are more sensitive, they are also more difficult to manufacture precisely. Machine heads may be open, with exposed gears, or closed, with a casing around all the gears. Geared pegs for violin family instruments also exist, although they have not gained wide use, which has to do with the extensive and irreversible physical modification that must be made to