Scoop of Fretless Bowed-string Fingerboards
Fretless bowed-string fingerboards are usually scooped lengthwise in a smooth curve, so that if a straight edge is held next to the board parallel to a string, some daylight will show between them, towards the centre of the board. Usually the scoop is slightly greater on the bass side, less on the treble side of the fingerboard. Different string materials or different styles of playing may call for differing amounts of scoop; with gut strings requiring the most, and solid steel-core strings the least. A typical full-size (4/4) violin with synthetic-core G, D, and A strings will show 0.75 mm of scoop under the G string, and between 0.5 mm and zero scoop under the E, which generally has a solid steel core on instruments with modern set-up.
On guitars, specifically steel-string and electric guitars, the relief (or "dip") is adjustable by altering the tension on the steel truss rod inside the neck. Relaxing the truss rod allows the pull of the strings to increase the dip, and vice-versa. Classical guitars do not need truss rods due to the lower tension of nylon strings, but should still exhibit some degree of dip.
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