The portion on which the first string is stopped being set back about a quarter of an inch.

This originated, in the early days of the banjo when the note E on the first string, alternating with F and with open-string D, occurred frequently as players seldom used more than the first few frets.

The keener-eared players noticed, however, that although D was perfectly in tune in the open-string G major chord, E was always sharp in the G,C,E chord in the first position. The setting back of the fret, of course, flattened the E to the right pitch and although this is not the proper remedy, one can understand why it was tried.

However, this device remained in use on expensive instruments many years later, when players were using the full range of the fingerboard.

To correct this a "tempered" tuning should be used:

Tune the 1^st string slightly flat so that when playing the open strings or barre chord the1st string will sound slightly flat but the 4.2.1.(F shape) and similar chords (where the 1st string is now only slightly sharp) will sound satisfactory.

The 5th string by tuning it very slightly flat, to stop the note predominating too much every time it is played. ^;