Among alternative guitar-tunings, regular tunings have equal musical intervals between the paired notes of their successive open strings. Regular tunings help beginning students to learn the fretboard's notes and chords. Regular tunings also facilitate improvisation by advanced guitarists.Guitar tunings assign pitches to the open strings of guitars. Tunings can be described by the particular pitches that are denoted by notes in Western music. By convention, the notes are ordered from lowest to highest. The standard tuning defines the string pitches as E, A, D, G, B, and E. Between the open-strings of the standard tuning are three perfect-fourths (E-A, A-D, D-G), then the major third G-B, and the fourth perfect-fourth B-E.In contrast, regular tunings have constant intervals between their successive open-strings: 4 semi-tones (major third): Major-thirds tuning, 5 semi-tones (perfect fourth): All-fourths tuning, 6 semi-tones (augmented fourth, tritone, or diminished fifth): Augmented-fourths tuning, 7 semi-tones (perfect fifth): All-fifths tuningFor the regular tunings, chords may be moved diagonally around the fretboard, indeed vertically for the repetitive regular tunings (minor thirds, major thirds, and augmented fourths). Regular tunings thus appeal to new guitarists and also to jazz-guitarists, whose improvisation is simplified. On the other hand, some conventional chords are easier to play in standard tuning than in regular tuning than in standard tuning. Left-handed guitarists may use the chord charts from one class of regular tunings for its left-handed tuning; for example, the chord charts for all-fifths tuning may be used for guitars strung with left-handed all-fourths tuning.The class of regular tunings has been named and described by Professor William Sethares. Sethares's 2001 chapter Regular tunings (in his revised 2010-2011 Alternate tuning guide) is the leading source for this article. This article's descriptions of particular regular-tunings use other sources also.