It is the most common tuning for the neck located furthest from the player on a two-neck console steel guitar or pedal steel guitar while a C6 neck is the one closer to the player.
This tuning has evolved in the last half of the twentieth century with input from prominent performers including Jimmy Day, Ralph Mooney and Buddy Emmons to support optimal chord and scale patterns across a single fret on the 10-string pedal steel guitar.
The Nashville standard E9 tuning was developed primarily from 1950 to 1970 during experimentation by elite steel guitarists.
In 1959, Ralph Mooney added a G♯ (a third interval) at the top end, making ten strings, also an enduring advancement.
[4] Buddy Emmons, in 1962 created a reentrant tuning by adding a D♯ (a major seventh) and F♯ (a ninth) at the top.