Size

This applies to both books and scores. The existence of a plus or double plus sign does not make the call number unique.

Non-plus = less than or equal to 26 cm. in any direction (height or width)

Plus = equal to or more than 27 cm. and up to or equal to 36 cm. in any direction (height or width)

Double-plus = equal to or more than 37 cm. in any direction (height or width)

M23, M219, M231: Yale practice for sonatas for piano, violin, and cello

The class numbers for sonatas for piano, violin, and violoncello are further subdivided:

All sonatas by one composer		Selected sonatas by one composer		Individual sonatas by one composer
M23	piano sonatas	M219	violin and piano sonatas	M231	cello and piano sonatas
M23.3	selected piano sonatas	M219.3	selected violin and piano sonatas	M231.3	selected cello and piano sonatas
M23.5^*	individual piano sonatas	M219.5^*	individual violin and piano sonatas	M231.5^*	individual cello and piano sonatas

^* Practice varies, but M23.5, M219.5, and M231.5 are used even when the composer has written only one sonata for that medium.

M175: Yale practice for solo marimba music

M175.X6: music for xylophone, marimba, vibraharp, vibraphone is divided into two separate class numbers:
M175.X6: xylophone, vibraharp, vibraphone
M175.X9: marimba

Application of this practice has varied in the past. Marimba music can be found in both M175.X6 and M175.X9.

ML410: Yale practice for composer biographies

The class number for individual composer biography and criticism and interpretation is further divided:

A101	= Writings, collected and selected
A102	= Correspondence
A103	= Autobiography
A104	= Single literary works
A105	= Anniversaries, festivals, congresses, etc.
A106	= Societies
A107	= Memorial volumes
A109	= Documents, interviews, etc.

Local practice in Class M

Size

M23, M219, M231: Yale practice for sonatas for piano, violin, and cello

M175: Yale practice for solo marimba music

ML410: Yale practice for composer biographies