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.
Guido of Arezzo
The "Micrologus", written at the cathedral at Arezzo and dedicated to Tedald, contains Guido's teaching method as it had developed by that time. Soon it had attracted the attention of Pope John XIX, who invited Guido to Rome. Most likely he went there in 1028, but he soon returned to Arezzo, due to his poor health. It was then that he announced in a letter to Michael of Pomposa ("") his discovery of the "ut–re–mi" musical mnemonic. Little is known of him after this time.