Topic summary
Fretboard
Extracted from the Wikipedia article Fingerboard.
Dip of guitar fretboards
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.