A bifolio that served as a pastedown in a book containing the Cathedral's altar and choir consuetudines. Now separated from the covers, but preserved in the original book as a flyleaf.

One piece is concordant with a hitherto-unidentified musical example quoted in the treatise De musica mensurata (1279) from St Emmeram.

Discovered in the autumn of 2011 by Santiago Ruiz Torres and Juan Pablo Rubio Sadia.

The right side of folio A is seriously mutilated. Folio B, which survived in a greater state of completeness, currently measures approximately 210 x 167 mm, with a writing-block of 175 x 115 mm. Such width points to a quarto format.

Staves ruled in red ink, c. 13mm, unusually (for this period in Spain) with a rastrum. The polyphony is copied in score though the music is not aligned vertically and at no time do the page-turns coincide in any of the four polyphonic parts. Texted beneath the bottom stave only.

No original foliation survives. Modern foliation A & B.

Red and blue initials.