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
Guitar tunings tuning and typically lowers the pitch ("drops") of only a single string, more common is the whole instrument and least common is two dropped strings (ie. DADGAD). This is almost always the lowest pitched (E) string on the guitar, although occasionally the A string may be lowered. The Drop D tuning, for example, is common in classical guitar and heavy metal music. For it, the low E string is tuned down one whole step, to a low D, and the rest of the guitar remains in standard tuning. This creates an 'open power chord' (three-note fifth) with the low three