By the 16th century, the guitar tuning of ADGBE had already been adopted in Western culture; a lower E was later added on the bottom as a sixth string. The result, known as "standard tuning", has the strings tuned from a low E, to a high E, traversing a two-octave range—EADGBE. This tuning is a series of ascending fourths (and a single major third) from low to high. The reason for ascending fourths is to accommodate four fingers on four frets up a scale before moving to the next string. This is musically convenient and physically comfortable and it eased the transition between fingering chords and playing scales. If the tuning contained all perfect fourths, the range would end up being two octaves plus one semitone; the high string would be an F, a dissonant half-step from the low E and much out of place.