Guitar Frets are laid out to accomplish an equal tempered division of the octave. Each set of twelve frets represents an octave. The twelfth fret divides the scale length exactly into two halves, and the 24th fret position divides one of those halves in half again. The ratio of the spacing of two consecutive frets is formula_1 (twelfth root of two). In practice, luthiers determine fret positions using the constant 17.817—an approximation to 1/(1-1/formula_1). If the nth fret is a distance x from the bridge, then the distance from the (n+1)th fret to the bridge is x-(x/17.817). Frets are available in
Eight-string guitar slew of new age progressive metal and djent artists. Seeking a guitar tuning that would facilitate jazz improvisation, Ralph Patt invented major-thirds tuning in 1963. Patt's tuning is a regular tuning, in the sense that all of the intervals between its successive open strings are major thirds; in contrast, standard guitar tuning has one major-third amid four fourths. Seven-string guitars are needed for major-thirds tuning to have the E-e' range of the standard tuning. Having an eight-string instrument allowed Patt's guitar to have G (equivalently A) as its open note. Patt purchased six-string archtop hollow-body guitars that were then modified