Slide-rule type devices for music study. Requires two printed parts that slide relative to each other; or three parts in the special case of a device for studying violin. Information on one of the parts is viewed through the other part. When employed together, the two parts reveal information most relevant in a particular musical scale or key, and obscure the information not normally used in that key. Multiple embodiments are possible, allowing a device to be constructed specific to a given instrument such as a violin or guitar, but the concept is not limited to stringed instruments, or any instrument. Similar devices could be made to facilitate music study for voice students, songwriters and arrangers. One of the sliding pieces is printed with all the available notes or tones, say, in the range of an instrument like a guitar. In the most likely embodiment, the other piece contains a transparent window printed with a series of geometric shapes of varying colors. These shapes are arranged in a pattern consistent with the scale type being studied and can be mapped to correspond to the layout on an instrument. They are colored such that a tone in a particular scale position is always in a particular color. The parts are indexed such that they can be aligned to show useful information in any key, including but not limited to all the possible voicings of the tonic chord, the most commonly used chords in that key, and chord variations that are based upon the major chord triad. This invention facilitates learning of simple music theory and the application of that theory to an instrument of choice. It is simple to use, easy to understand, and different in many respects from other such devices in the prior art, as will be discussed in the specification.