This paper examines the role of annotation in coordinating Western Art Music (WAM) performance. Annotations were obtained from a performance score drawn from an instrumental case study of ensemble performance. The case study consisted of nine videotaped rehearsals and a performance of Torû Takemitsus Masque for Two Flutes (1959-1960). A prior analysis of the conversation, body motion, and instrumental play revealed four domains of coordination. This paper presents a detailed exploration of one of those domains, annotation, using theory drawn from the field of distributed cognition. The annotations were classified by their function in supporting cognitive and meta-cognitive processes of performance in relation to the printed score (visual salience, repair/correction, and anchoring). The classification supports theory in distributed cognition by demonstrating a clear functional relation between the annotated score and both internal and external performance processes.