In Medieval music, the Guidonian hand was a mnemonic device used to assist singers in learning to sight-sing.

Guidonian Hand: a mnemonic device used to learn how to sight-sing medieval music

Late medieval score by jkervinen, via Flickr

Late medieval score by jkervinen. XD I can just see some poor sucker in those times trying to read this sheet music

Boethius, De Musica, c1350

"Allegory of Music" Boethius: De arithmetica, De musica c. 1350 Manuscript (V. century Colorful cote-hardies with sleeve extensions, long hanging lappets. The Medieval music instruments: Vielle;

Christian and Muslim playing lutes in a miniature from Cantigas de Santa Maria of Alfonso X.

Christian and Muslim playing ouds Catinas de Santa Maria by king Alfonso X - Moors - Wikipedia, the free encyclopedia