This paper presents a developing Pitch Error Coding Protocol for assessing the accuracy of a musician’s performance. The protocol organized performance errors into any of three main categories, each based on an established cognitive theory of music memory and processing: (1) the Serial Distance Hypothesis (SDH); (2) the Implication Realization (I-R) model; and (3) the mental organizing principle of the Schema Theory (SCH). An elite oboist formed the basis of a detailed case study where his sight reading, practice, and performance of a challenging excerpt of music were examined. These data were used to: 1) investigate the protocol; 2) ask whether any protocol components could explain errors better than others; 3) and show where improvements after practice occurred. The results revealed that the SDH accounted for the majority of pitch errors, these originated in a three-note proximity of the target and some SDH errors overlapped with the I-R category errors. Although final counts for SDH and I-R are similar, SDH uniquely identified errors more frequently than the I-R. Future research and development of the protocol might look at combinations of pieces and performer to determine whether SDH may be a dominant source of error.