Among alternative tunings for guitar, each augmented-fourths tuning is a regular tuning in which the musical intervals between successive open-string notes are each augmented fourths. Because augmented fourths are alternatively called "tritones" ("tri-tones") or "diminished fifths", augmented-fourths tuning is also called tritone tuning or diminished-fifths tuning. The standard guitar-tuning E-A-d-g-b'-e' interjects exactly one major third amid four perfect fourths for the intervals between its successive open strings. In contrast, the augmented fourths tunings C-F♯-c-f♯-c'-f '♯ andB-F-b-f-b'-f'