This article investigates the correctable technologies for musical drafts available to composers during the central and later Middle Ages (twelfth-fifteenth centuries). The starting point is a unique passage from the autobiography of Renier, abbot of St Laurence of Liège (c. 1110/20-90), which clearly describes someone sight-reading a new work from the text and musical notation entered on wax tablets (an edition and translation of the passage are provided). Additional musical references to wax tablets are discussed, as are references to other correctable technologies (text supports and appropriate styli) potentially available to composers, such as varieties of sleeked pasteboard, slate tablets, lead used directly on paper or parchment, liquid correcting fluid or powder or paste, and composition in the mind. Descriptions from the contemporary technical literature, archaeological and iconographical evidence are briefly presented. An estimate of the relative prevalence of these techniques is ventured with references to aspects of the technologies and their musical application which require further investigation.