This chapter describes larger projects by focusing on an especially poorly studied area, musical erasures in late medieval books, in order to suggest the potentially vast contribution of a paleography of square notation. A potentially rich area within a paleography of square notation is that of musical erasures. An investigation into erasures is not only useful in and of itself, but offers insights into medieval musical repertoires, thus demonstrating the potential of the broader and much needed project of a paleography of square notation. There are distinct kinds of musical copying errors leading to scribal erasure and correction. They can be categorized into five general types, by order of frequency: transposition, misalignment, omission, repetition and substitution. In the error of omission, the scribe has skipped over a part of the musical text. Thirteenth-century musical erasures are a direct result of copying conditions and environment.