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 Acqui
He was born around 1004 to a noble family of the area of Acqui, the Counts of Acquesana, in Melazzo where the family’s wealth was concentrated. He completed his education, by now an orphan, in Bologna. Elected bishop of Acqui in March 1034, his career was marked by reform in the areas of liturgy, spirituality and morality. He was generous in donating his own money and possessions to the diocese, in part to remove the economic pressure which had led to widespread corruption, and in part to support new projects. The latter included the promotion of the education of young women and the foundation of the nunnery of Santa Maria De Campis. Under his government, too, Acqui Cathedral was erected, dedicated to the Madonna Assunta and consecrated on 13 November 1067.