Guidonian hand
In Medieval music, the Guidonian hand was a mnemonic device used to assist singers in learning to sight-sing. Some form of the device may have been used by Guido of Arezzo, a medieval music theorist who wrote a number of treatises, including one instructing singers in sightreading. The hand occurs in some manuscripts before Guido's time as a tool to find the semitone; it does not have the depicted form until the 12th century. Sigebertus Gemblacensis in 1105–10 did describe Guido using the joints of the hand to aid in teaching his hexachord. The Guidonian hand is closely linked with Guido's new ideas about how to learn music, including the use of hexachords, and the first known Western use of solfege.
Mandobass
Up until 1911, the mandolin family of instruments as known in the United States had no true bass member. Mandolins were relatively new to the United States, beginning to be known in the mid-1880s and reaching the peak of popularity before 1910. The American public was mostly unaware of the few mando-basses being made in Europe. Published minutes from the 1911 meeting of the "American Guild of Banjoists, Mandolinists and Guitarists" included an entry about bass mandolins developed in Britain, and indicate that issues related to the mando-bass were among the first discussed at the meeting. It was at this meeting that George D. Laurian of the Gibson Mandolin-Guitar Company announced that his department had developed a bass member for the mandolin family.
At the Guild's next meeting in 1912, four companies displayed their versions of a mando-bass: Gibson, Leland, Vega, and Wm. C. Stahl. All four companies advertised extensively, but in contrast to its competitors, only Gibson promoted their mando-bass in photographs of musicians playing it in large groups, emphasizing the social aspects of playing their instrument. Ultimately, the two most successful instruments were those produced by Gibson and Vega.