Unusual Guitar

A guitar using this tuning can tune to itself using the fact, with a single exception, that the 5th fret on one string is the same note as the next open string; that is, a 5th-fret note on the sixth string is the same note as the open fifth string. The exception is the interval between the second and third strings, in which the 4th-fret note on the third string is equivalent to the open second string.
Standard tuning has evolved to provide a good compromise between simple fingering for many chords and the ability to play common scales with minimal left hand movement. Uniquely, the guitar's tuning allows for repeatable patterns, which also facilitates the ease of playing common scales. There are also a variety of commonly used alternate tunings. Most of these are open tunings, i.e., the unfretted strings produce a simple chord, such as a G Major chord. Many open tunings, where all of the strings are tuned to a similar note or chord, are popular for slide guitar playing. Alternate tunings are used for two main reasons: the ease of playing and the variation in tone that can be achieved.
Many guitarists use a long established, centuries-old tuning variation where the lowest string is 'dropped' down a whole tone. Known as Drop-D (or dropped D) tuning it is, from low to high, DADGBE. This allows for open string tonic and dominant basses in the keys of D and D minor. It also enables simple fifths (powerchords) to be more easily played. Eddie Van Halen sometimes uses a device known as a 'D Tuna,' which he patented. It is a small lever, attached to the fine tuner of the 6th string on a Floyd Rose tremolo, which allows him to easily drop that string from E to D. Many contemporary rock bands retune all strings by several semi-tones, making, for example, Drop-C or Drop-B tunings, However this terminology is inconsistent with that of "drop-D" as "drop-D" refers to dropping a single string to the named pitch. Often these new tunings are also simply referred to as the "Standard" of the note in question e.g.–"D Standard" (DGcfad').