What is the purpose of ledger lines in music notation?

The purpose of ledger lines in music notation is to indicate pitch above or below the staff. Ledger lines are short lines added above or below the standard staff to extend it vertically, allowing for the notation of pitches that are outside the range covered by the five staff lines. For instance, in a treble clef, the notes above the upper staff line or below the lower staff line can be represented clearly with ledger lines, thereby enabling musicians to read and perform a wider range of notes accurately. This system ensures that even high or low pitches can be notated without compromising the clarity or organization of the musical score.

The other options address different aspects of music notation. While separating measures is indeed important for indicating musical structure, it is accomplished through bar lines rather than ledger lines. Dynamics, which indicate the volume and intensity of a musical piece, are represented using specific symbols and markings on the staff, not ledger lines. Lastly, rhythm values are depicted through note shapes and stem directions, separating them from the function of ledger lines, which is solely focused on pitch.