Guidonian hand

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 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.

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[broken anchor] to the E at the top of the treble clef[broken anchor]).

Exact notation to the hexachord system can be found in a reproduction of Ameri Practica artis musice (1271),[3] or in the 1784 source Scriptores ecclesiastici de musica sacra potissimum.

[4] The hexachord as a mnemonic device was first described by Guido of Arezzo, in his Epistola de ignoto cantu and the treatise titled Micrologus.

Over time, the soft and hard variants of 'b' were depicted as a rounded '♭' and a squared-off '♮' which gradually developed into the modern flat and natural signs (or, in Northern Europe, into the letters 'b' and 'h').