Guido of Arezzo
In the 12th century, a development in teaching and learning music in a more efficient manner had arisen. Guido of Arezzo's alleged development of the Guidonian hand, more than a hundred years after his death, allowed for musicians to label a specific joint or fingertip with the gamut (also referred to as the hexachord in the modern era). Using specific joints of the hand and fingertips transformed the way one would learn and memorize solmization syllables. Not only did the Guidonian hand become a standard use in preparing music in the 12th century, its popularity grew more widespread well into the 17th and 18th century. The knowledge and use of the Guidonian hand would allow a musician to simply transpose, identify intervals, and aid in use of notation and the creation of new music. Musicians were able to sing and memorize longer sections of music and counterpoint during performances and the amount of time spent diminished dramatically.
Dionisio Aguado y García
Aguado's major work "Escuela de Guitarra" was a guitar tutorial published in 1825. As of 2011, it is still in print, with Tecla Editions releasing a reprint in 2005. In the "Escuela" Aguado describes his use of fingernails on the right hand as well as his invention of a "tripodison": a device that held the guitar and thus minimized the damping effect of the player's body on the guitar's back and sides. Aguado's other works include "Trois Rondos Brillants" (Opus 2), "Le Menuet Affandangado" (Opus 15), "Le Fandango Varie" (Opus 16), as well as numerous waltzes, minuets, and other light pieces. The more extended works require a virtuoso technique and left-hand stretches that are almost impossible on the longer string lengths of modern guitars. (See Frederick Noad, "The Classical Guitar")