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 1105–1110 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 solfège. Theory The idea of the Guidonian hand is that each portion of the hand represents a specific note within the hexachord system, which spans nearly three octaves from "Γ ut" (that is, "Gamma ut") (the contraction of which is "Gamut", which can refer to the entire span) to "E la" (in other words, from the G at the bottom of the modern bass clef to the E at the top of the treble clef). The compound names combine the tone's pitch letter and up to three hexachordal syllables to indicate the functions of each note. These compound names were sometimes rendered with spaces between the pitch letter and the syllables, but in prose were also sometimes combined into one word, adding an "e" after the pitch letter if it was a consonant, yielding the names indicated in the chart below. Some of the compound names clarify the register (for example, C fa ut, C sol fa ut, and C sol fa indicate three different octaves of C), but there are also some names that repeat (for instance, the same name B mi appears in three different octaves). In teaching, an instructor would indicate a series of notes for their students to sing by pointing to them on their hand, similar to the system of hand signals sometimes used in conjunction with solfège. Commonly, as in the example below, the notes of the gamut were mentally superimposed onto the joints and fingertips of the left hand. Thus "gamma ut" (two Gs below middle C) was the tip of the thumb, A ("A re") was the inside of the thumb knuckle, B ("B mi") was the joint at the base of