A tuning apparatus for a stringed musical instrument is provided. The apparatus includes a dual-action cam clamp assembly and a plurality of string-contacting members with easy-to-adjust rocker arms. The dual-action cam clamp assembly removably attaches to a desired longitudinal position on the instrument's neck. Each of the string-contacting members is rotatably supported by a rocker arm shaft, and the easy-to-adjust rocker arms are adapted to rotate about the longitudinal axis of a two-part shaft of the clamp assembly independently of the other string-contacting members. Each member also adjustably impinges upon and urges a given string or course thereof on the instrument toward a user-selectable one of three different longitudinal positions on the neck's front surface, these positions including a home position, a home−1 position, and a home+1 position.