An instructional and reference device, for use by violinists, violists, and cellists, is constructed using an outer sleeve or pocket with a sliding panel. The outer sleeve has a larger and a smaller opening, each positioned to reveal information imprinted on the sliding panel. The information revealed through the smaller opening may include musical keys and key signatures. The outer sleeve is imprinted with the names of the strings above the larger opening, through which is revealed the appropriate fingering used on each string when playing in the musical key displayed in the smaller opening of the outer sleeve. Several different inner panels can be used in this musical slide rule, making available fingering information relevant to violin, viola, cello, and/or variants thereof, for different hand positions on these instruments; different inner panels can be used to display fingering information for various positions on the fingerboards of these instruments. Fingering for classical scales of major and minor keys for various modes, and ethnic and stylistic scale patterns, such as are used in jazz, blues, and musical styles native to subcultures around the world may be provided. The inner panel displays the numbers of the appropriate fingers on each string, their relative spacing on each string in each selected musical key, and through various colors or other means may indicate the locations of the root notes of each major and minor key, and arpeggio notes.